Should you buy?
I bought a used '88 260E about a year and a half ago with 120k miles and it has been a fantastic car.
A few of the common problems with the w124/m103 are:
1. Oil leaking from upper front timing cover (easy to fix)
2. Oil consumption due to leaking valve stem seals (easy to fix)
3. A/C and climate control problems (not always easy to fix)
4. Cruise control problems
The biggest factor in any used car is condition and how well it has been maintained.