Rust is always hidden and can be prevented or slowed down at the lower rear window seal .It creeps along slowley under the gasket until its too late .Reason from what ive recognized as the culpriet is the chrome gasket holder and a weathered seal.Ive been putting a small amount of clear silicon at the chrome joint then a small amount along the window and seal ,then body and seal .Its a very common 300cd issue.
I also have that color on my 84 coupe ,this vehicle sat at a used car lot and was bought with a 1994 sticker,yours faired much better than mine , alot of time sitting in a garage Im sure.Im located just north of houston and recommend a mercedes meet which usually happens in June .The Austin ,Dallas ,and Houston guys and gals join up to meet at the town of Centerville off I-45, we should bring the coupes and talk shop.

OK I think thats Gearheads coupe-- and this is the OTHER coupe He told me about --ruchardson /garland area-- so there is one LESS burgendy one, but chasinthesun has one so ~ There are still Three that I know of in Texas.
The parts car- is still got a complete hvac box in it and also a good transmission. I have one good rear glass but those are pricy-Hard to find a nice pair of doors, complete side bright trim window surrounds, trunk and hood,
all the other stuff im keeping for when brakes regulators etc go out on me.

I wish you could find rubber window seals for these! I really want some. Oh and this meet up is in June right? My friend told be about it today (he has an account on here) He has the grey CD in one of my pics above! Well him and a handful of his friends in the area go to them every year so i will be part or the convoy this year Really looking forward to it!

Yes that is Gearheads CD! How much for the hvac box? Just curious? any interior pieces in palimino?

I have a nice drivers seat in palomino. I have nice seat bases /good springs and FOAM bunz instead of horsehair--That makes aworld of difference in comfort. and a few bits like door pulls etc.
the complete hvac is $100 with the dash control unit included.

Hmm

Anyway I ran into GH at the FW pnp last month when he mentioned his neighbor had this coupe just like mine--He said it needed door strikers (parts in the door jam) and I can supply those too.

Haha, i think that was me he was talking about. Is his name Darrell?

uh yea --darrel is his name o

Yep, he is my neighbor well a few blocks away (walking distance)