My mechanic is telling me that the slamming noise from the rear wheel well is NOT the shock, the shock itself looks OK, he says that it appears that there is a donut or bushing between the shock and the body which isolates and quiets the shock a little which is worn/ gone.

Anybody know where I can get this?
I can't find it in any parts books/ catalogs which I have.

Oh, this is my '81 300TD with SLS.