w123 brake booster--supposed to be fluid filled?
 

usually when i remove a brake booster, it's pretty much empty--this is normal, right? the other day i removed a w123 brake booster only to find it was filled with brake fluid. does this mean a leak on the master cylinder seal that leaked fluid into the booster, or is this a fault of the booster itself?

Correct, and because it is brake fluid, the diaphragm in the booster is likely toast, and the casing will rust horribly quick, because it's eaten any and all coating inside. The attached master cylinder however, I suspect can be rebuilt, but it's probably cheaper to find another used one.

The problem is caused by the master cylinder, not the booster.

so, generally speaking, if any amount of fluid is found inside the booster after removing the mc and just unbolting the booster, does that means that the booster is potentially still good, but probably bad?

It is potentially still good. I had this happen on my 83 recently...in the last couple of years. I sucked out all the fluid I could and put on a new mc and the booster is still going strong.

potentially still good... well, still functional.
but for something as critical as brakes, I'd err on the side of caution, and not tempt fate or murphy with a life threatening failure.

Boosters are not cheap. I'd at least experiment with the existing one to see if it is still functional. You won't completely lose your brakes if it fails. You can still use the brakes but it will probably take both feet to make a quick stop.

Oh, the Irony! I get out to the car this morning, pull out of my parking spot and go to brake, and it's all mush. MY MC is now leaking into my booster :mad:
Luckily I have the other from my SD :D it's just a pain in the arse to change...
I'll check out the leak and see if I can salvage the booster..I have another MC.