My head gasket blew at 145000 miles.
I had to replace the engine block.
I had to have the heads machined four times in 5 months.
Rear axel disconnected from body at a high speed.
This car has been a problem car since the day I bought it. I keep it in running condition because not only is it my first car, but I love it to death. I will never buy another Mercedes and I soon plan to drive this one off a cliff if it costs me any more money.
Read the comments of the other proprietors of Mercedes W123. You are the only who have had so serious problems, you would have to consider the age of the car, the care and use that the previous owners give him.
It is a very noble vehicle. By something still wheel in many African countries and in the Middle East, by its reliability.
I agree with the above commenter. I purchased a 1977 230 euro sedan with 268,000kms and so far even before I've got it registered for the road I've had to put $800 into items that should have been replaced by the last owner. (flex disc's which caused your drive-shaft failure) fuel pump, starter, f/r springs, shocks, trailing arm, tie rods, disc's and pads, tune-up parts and there is more to do.
But I know from even yard driving it now I will have a vehicle that will be a comfortable, great handling car that will be rock solid reliable. Easy to fix with the right metric tools and a blast to drive.
Don't give up, spend a little money on maintenance and you will love it to death.