I have an 83' 500sl I picked up in January. The name of the importer on mine is inside the drivers side door jamb,near the tire pressure table. I haven't had problems finding parts either here or at the dealer but you have to make sure they understand it's a euro version. Easiest way is to give them the VIN 107046....
I'm in the computer industry so I do a lot of information searching and purchasing online. This becomes difficult because as soon as you enter in 83 model year their automated system only allows for the 380. You either have to call or look somewhere else.
See if the records reflect if and when the timing chain and tensioner were replaced.

Hope this helps.

Marc