I have one, make sure you check for the rust. My car is still in the shop to get all the minor rust spots removed. I was amazed at how nice it looked. They did a really good job!
The rear windows... make sure they work. I can hardly find a regulator for the rear windows...
Everything else, I guess the normal stuff (Transmission, engine, etc.)
Here's my take...
1. Transmission : It shifts noticeably when the engine is cold, but once it warms up, at least mine, shifts VERY smooth and precise. I love these cars.. I expected much less from a 20yr old.
2. Engine : Mine seems to start even when the air is 20F (probably the coldest it ever got in Boston...) with just one pre-glow.
You have to drive it, these cars aren't E55's... but they certainly aren't that slow to a point that they're dangerous when merging onto highways...
As usual with the W123, air conditioner... I need to get mine converted before summer... most places wouldn't recharge R12 anymore...
Check the window seals.
Oh well wait for the experts..
Cheers,
-Holson-