I am in much the same boat as Robert Roe. Bought 300sd with 200K two years ago. My skills are limited to changing the oil which I do religiously; everything else goes to mechanic.

Here's what's wrong right away -Windshield leaks front & Rear. Minimal rust.

Car has a very rough rear gear just recently...vibrates and loud. All other shifts are fine.

Mechanic tells me I need new motor mounts and primer pump (leaking)

airconditioning blows out of windshield vents and blows hot. Heat has been working fine in winter.

glow plug light just stopped working a week ago but I replaced them when I first bought the car. Think that they are OK.

My rule of thumb is to maintaini the easy stuff - brakes, oil changes, tires and budget $1000 a yea for other stuff. Just replaced the center driveshaft support

car has a creaky noise in right front when steering, not too loud but noticeable

main concern is the transmission. Have read the windshield seals posts exhaustively and will fix shortly if transmission OK. Would like A/C but can live without it if I have to. (Seems every other sd I see this summer has the same problem since they all drive with the windows down)

Thoughts?

If you try to sell your car and intend to disclose
all the imperfections, get ready to take a loss.
You did not mention what you paid or what you'd
want to get for it, but I can't sell my 82' 300SD
which I paid $1000 last year and have since put
a new trans and much more >+$3,000. I am so
sick of getting emails asking if I'd take $500
instead of a $1,000. It has a little rust and 280k
miles, people don't realize this mileage does not
mean the end is near if they are unfamiliar with
mercedes diesels. I'm going to stop all the ads
trying to sell the car soon to end the aggrevation.
Hence, I'm keeping mine. Fix what you can and
live with the rest, part it out if it breaks beyond
practical repair. Good luck!