I think you are right. I saw something like ET215 and had trouble interpreting what this meant. Searching through other posts here I thought it might be 25mm for the W126 rather than a 21.5 mm offset. (Perhaps there are different offsets between some of the W126 class car models?)

But your post cleared up that misunderstanding - thanks!

I have been searching all over the web for a matrix of what offset goes with each model Mercedes in terms of OEM wheels. It seems to also be dependent on model year, and of course the size of the wheels vary too.

At some point I'll get a chance to post a picture to show the effect.

Ken300D