Wow, that is an awesome analysis of the process! I"m only a new member, so I have no juice, but this would be a really useful addition to the section here that gives you directions on how to do a variety of projects!!!
I did see that the really large rear bolts, although shorter than the others, did have some rounding off on the heads. That kind of worries me that someone was monkeying around with the subjframe after the accident when they replaced the axle. Why leave it (or maybe it shifted) with the subframe out of spec is a mystery but I'm worried that the bolts have been damaged.
On the plus side, the car is from Florida so corrosion or rust on the outside is not something that i've seen underneath.
I will, of course, follow the advice to back it out by hand slowly going back and forth to make sure that I don't encounter one of these issues as referenced.
I do have an advantage in that the lift and place I'll be working has the benefit of retired mechanic who had his own shop (a foreign car repair shop) so, what he doesn't know about BMW's isn't worth knowing. That said, his mechanical knowledge is amazing.
So, the operative idea then is be slow and methodical, lubing the bolt and seeing what it does. I definitely don't want to break it off and then engage that nightmare of having to get into the captive nut!
Thank you for your incisive analysis on how to do this! I'll follow up with the results!!

 

Rounded bolt heads makes me think someone recognized need to loosen bolts to realign subframe, but couldn't loosen them, or at least not all of them, so gave up.

Hopefully that was simply bc they were idiots and using wrong tools (like SAE sockets instead of metric, not quite right fit, etc).

Hopefully you won't run into situation where rounded bolt heads makes them difficult to remove. An old mechanic is perfect person to address that. He'll know tricks. Like hammering on a slightly too small socket, which both makes a solid fit, and tends to break stubborn threads free.

I wouldn't be opposed to using a gun to bust them free. Sudden sharp impacts better at breaking fasteners free vs increasing torque from a long socket wrench and muscle.

But don't use gun to remove them, just to break them free. Unless they're coming out like butter. Or if there are skilled hands that can modulate trigger so you get ease of removal without risk of binding and breaking. At low power, gun will stop before threads to bound to save.

Full throttle to bust em free, modulated trigger to slowly zip em out.

 

OK, that makes sense...bust loose with a gun but take them out with the the wrench unless they are coming loose easily with the impact. I'm still a bit wary of the impact, but I can see the point of modulating pressure. He'll know what that is all about.
He laughted when I asked him about the stuck bolt syndrome. First he told me I worry too much (I do) but then he said could have been anything, rust in the threads, etc. Like you said, wrong socket....which was only tried on one of the large bolts, the two in the rear.
So, probably work on this next week....this weekend is the classic German car festival in Norcross, GA, so we won't be around on Saturday.
I'm avoiding driving it as I think the valves, never adjusted from the CARFAX, might be too tight...exhaust valves from what I read. So, undercarriage bolts, valve adjustment, alignment and various lubricants. Much to do.

 

Make sure do valve adjustment on dead cold engine.

Since its dbw, these run lean, should set exhaust valves to loosest end of range. Note, tight valves are quiet, correctly adjusted are noisy. Don't be worried if a little more clatter afterwards.

Following the service manual for this procedure is needlessly complicated, regarding how to manually turn engine to exact spot to adjust each set of valves. Align thjs timi mark, then turn this many degrees, then this many more, etc.

Leaves room for human error. Amuch easier and virtually error free way is to jist turn crank (always only fwd direction only, clockwise) until valves you wanna adjust next have their cam lobes pointed up,180 degrees away from followers (the thing cam lobe pushes on to open valves).

I call this method 180 away.

There is no real precision required for this part of the task. So long as cam lobes pointed up away, you're good.

Even if you want to count degrees of turn, use 180 away to validate no mistakes were made. If lobe not 180 away, don't adjust that one. Start over.

All the precision for this task is the actual adjustment, how loose or tight you adjust against feeler gauge.

 

OK, I was going to ask you about the valve adjustment as I read your post in that valve adjustment posting. Its several years old and I was wondering if there was an update, but you explained it in even more detail here. I have downloaded, I think, Rob Robinette's posting on valve adjustment but I think if I showed it to my friend, he's not really going to look at it too closely.
I think your method is fairly easy to assimilate and will make short work of it. I don't have a feel for the feeler blades, but I'm sure my friend will show me.

This is certainly an experience, working on this car. I'm hoping to get the valve adjustment done, the subframe bolts, alignment and then new tires. Tires on oe side are worn out and a different brand from the oK, Pirelli's on the other side. I'm wondering if that is why my VSA light keeps going off after driving about a mile. Once I turn the car off, it goes away and then doesn't come back until I start and drive the car for a bit. Wonder if it is the tires!

 

VSA works off the anti-lock brake system sensors which detect wheel rotation speeds and applies selective wheel braking and throttle to correct mismatches. The system assumes matched tires which you don't have. Different brands, patterns, age (tread wear), and even pressures can upset the feature. Like any computer "garbage in garbage out" applies. "Best tires" is a constant topic here. For maximum enjoyment I recommend Extreme Performance summer tires in OEM, maybe "CR" sizes. Yeah they wear quickly. So what?, these are toy cars made for fun. 10K or 11K miles has been my experience but that's 3 or 4 years of driving for me.

Summer tire grading (higher to lower) is Extreme, Max, Ultra High. Ultra High is 3d tier but there are still some good, but not great, tires like the Firestone Firehawk Indy 500 tires in that category.

-- Chuck

 

Thanks Chuck, as you might have seen, Car Analogy and I have had a lively discussion, more educational imparting of knowledge on his part referencing the actual mechanics! That said, I've got a set of Conti's on order, the extreme summer tires, so once I can get that subframe issue fixed, I'll get it in for an alignment and then have the new tires mounted. At least that's the plan...hopefully that will solve the VSA issue.

 

Which Continentals are Extreme Performance Summer tires? I can find Max Performance (second tier) Continental ExtremeContact Sport 02 .

-- Chuck

 

I believe those are the ones. I have them on an E46 BMW (I believe) and they seem to do fine.