Yes that oil should not go in any S2000 differential, change it as soon as possible before you damage your diff.
Hypoid Gear Oil SAE90 GL5 is the correct Honda oil, part number here in Europe is 08294-99901HE not sure if it's the same in the US though.

 

Pretty sure they don't carry the correct diff fluid at Honda dealerships around here anymore and haven't for some time now. Your best bet is to go to the auto parts store and buy some 75w-90, 75w-110, or 75w-140 synthetic gear oil and either have your go to service department take car of it, or do it yourself. It is a very simple procedure as long as you have the right tools. A lot of people use Mobil 1 75w-90 LS Gear oil, as it is readily available.

 

Looked at your owner's manual? Note the SAE 90 spec from 10 year ago is now about SAE 110 so 90 is too thin and 85 even thinner.

My gearbox and differential choices. Note the diff oil spec (110).



-- Chuck

 

This should be a lesson to you about bringing your car to the dealer for service. DON'T DO IT!

They don't know these cars, but they assume anything they do must be correct simply because they are the authority. When you go back to them and point out their mistake, their reaction won't be to apologize, to tell you they will fix it. They will say you are wrong. If you tell them an Internet forum gave you the info, they will ridicule us, and you for listening.

No matter what, get this fluid out and correct stuff in very soon. Don't drive the car with that stuff in our your will kill your diff.

 

Maybe refine that a bit to say that you should stay away from a dealer, or any shop for that matter, unless you are certain there is someone working on your car who has real experience working on S2ks. This is a real issue I agree and it it becoming increasingly difficult to find good experienced s2k mechanics.

 

If there is a really good mechanic with S experience at a dealership, will that be the guy that works on your car? Even if you insist? Even if they assure you that will be the guy? I wouldn't trust a dealership as far as I could throw them...

 

I agree generally, but I am fortunate to have a dealership with a good mechanic and he owns and loves his S and they can be trusted. I agree - it is the rare exception.

 

Honda really dropped the ball on this diff fluid debacle.

amsoil 75w110 if you want more protection. 75w140 for even more.

75w90 for convenience since it's more widely available.