Here's the deal....when your car was made the oil called for by Benz was to have a rating of CD. Back then gas engines called for SF (well maybe it was SG). Today we are up to SJ or better. SJ exceeds CD So on the one hand you are ok with GTX on the other hand there is even better than what Benz called for back then. I think it is safe to assume that if CH-4 were available back then, Benz would've wanted you to use it.
( I think I just clouded the issue some more
03/83 300D 184k
07/73 280 160k