I just inherited a '90 626 with auto tranny from my aunt and I am trying to work through the problems with this car since it has been sitting for a while.
The car has 123000 miles and looks good on the outside and inside, with the exception of bald, mismatched tires. Maintenance was spotty everywhere else though. Some problems that I found are:
(1) Radiator has a big hole (fixed)

(2) Brake pedal was sinking all the way to the floor with engine running. I suspected a leaky master cylinder after I noticed brake fluid around the cup and the fluid was a milky white with particles floating around in there. After I had installed and flushed out the system, the brake pedal seemed firm. It was only then that I noticed the rubber boot on one of the calipers was torn. I then proceeded to replace both calipers in the front. I used a technique I learned somewhere where you depress the brake pedal before opening the lines to prevent air from getting back into the master cylinder. The only problem is I think air got back in somehow. I have bled the brakes for a full hour with my one man bleeder kit, and even after seeing no bubbles, the brake pedal goes all the way to the floor before I feel any resistance. I also noticed that the rpms will drop when I press the brake pedal with the car idling. Might I have air in the master cylinder that needs to come out? How do I bleed the master cylinder while it is on the car?

(3) The parking brake cable is rusted to hell and has snapped. Is the parking brake cable required to be there to adjust the rear drum brakes? I didn't see any way to adjust the rear brakes otherwise. The wheel cylinders look fine, but I am not sure if they can still be bad anyway. The brake shoes also looked fine.

(4) While I was under the car to change the brakes and radiator, I noticed black oil around the transmission pan. I also noticed black oil leaking out when I removed what looks like the tranny oil return hose to the radiator. I tried to check the level on the dipstick, but I didn't even get a reading. Also, whenever I put the car in park, it makes a grinding sound. I am assuming that the tranny might have major problems if the fluid has turned black. Can anyone tell me which hose is the oil return hose that goes to the radiator from the tranny? I see two small hoses that attach to the bottom of the radiator and don't have a repair manual to tell what is what.
Also, how am I supposed to flush the tranny fluid on this car?

(5) The last problem is the most perplexing. When I checked oil level on a cold engine, it was about a quart above the full line. Can that cause a problem? I noticed that there is some oil around the valve cover and the engine makes a loud ticking noise. There is also some rough idling. If it is nothing serious, I can leave this at the bottom of the list.

I know this is a long post, but I have to assume that everything is broken on this car. But I figured since I got it for free, it can't hurt to get it running. I can do almost anything except rebuild the tranny.