There really isn't much that could go wrong w/ these things:
watch for rust
check that the rear axle boots aren't torn
drive the car make sure it doesn't vibrate at 60-80mph.
it shouldn't make any clunks or groaning noises of any sort - very smooth car for its age.
check that windows roll up and down correctly (be them power or manual)
make sure the electric sunroof works
check that A/C works (the 240's dont have the kind of useless ACC)
check condition of fluids (diesel oil would be black in no time)
check the brakes
check steering wheel for play - there should be little to none
shouldnt smoke excessively
should start right up after the glow cycle.
good luck! 123s are really the corolla of MB I think
tough cars!
but it's got more class and looks obviously :p