If you do a search on a thread i wrote it vaguely shows you how/what to change.

 

I had this exact same issue 4 years ago.
Took me a while to track down a second hand actuator (£20 IIRC).
It worked for a few months but started to be troublesome again with not just the driver's side failing but the passenger too. Hence I bit the bullet and forked out £150 for 2 new ones and not had the problem since.
The issue is with the little motor in the actuator. It effectively didn't have the power anymore to rotate the actuator. I greased the wormgear in the actuator as that might have been the reason why the motor was having trouble but even after that the motor wasn't up to the job - and the actuator wasn't tight so there was no resistance really. It's not too dissimilar to the sort of motor you get in Scalextric cars for those of you familiar with those but it's quite a torquey little thing. I looked (but not very hard) for a motor replacement but since there's no such thing as a proper electrical store as would have probably been around 40 years ago that stocked everything from motor bearings to generators, I gave up and sadly conceded defeat. It's blooming typical that the faulty part is probably a few quid if that yet you need to buy the whole assembly as they don't sell the motor individually.
If there are any sparkys out there maybe you have an idea what would cause it.
Hope that helps, if only to prepare you for what to expect in future.

 

with the above.

I tried the same as you and had no luck. The motor had virtually reached the end of its life.

Here are some pictures to help...

 

When I swapped my actuators I managed to do it without removing the door lock mechanisms themselves. You can unscrew the black/grey plastic cowling which gives you full access to the actuator and the ability to negotiate it free from the linkage.
I little more fiddly but I figured on minimising what I removed at the time.
Just a different way of doing it I guess rather than better or worse.

 

I couldn't get my bloody hands in and negotiate the screwdriver .

I suspect the passenger side actuator may follow soon as you say.

 

You guys rule. Thanks for the help!!!