I have a '89 260E with well over 400K on the clock.
I bought it back in 1991 (17 years ago)
A/C evaporator: Still with the original in place.
Transmission: Still with the original in place. Never been opened.
Head Gasket: Replaced at 275K when I had to fix the valve guide problem. (valve cover replaced at that time.
Radiator: Replaced at around 300K (broken upper neck)
These are very tough cars.
Good luck