After I last posted, I ended up installing the new MC I ordered and I did not install the JY booster/MC assembly as the booster was a different model and I already had a new MC on hand.

The car has been parked in my driveway under a cover for the last 4 months. Yesterday it was warm and I removed the cover and opened the hood. Sure enough, no fluid in the reservoir, big puddle under the booster. I removed everything from the car. There was oil in the booster obviously.

Here's what I noticed/understood/know:

-The MC is bad because the seal allows fluid to be pulled in the booster
-The booster leaks the fluid from the bottom, hence the booster is also defective
-The booster still held a small amount of vacuum even if the car was parked for 4 months and the brakes always felt OK before that, therefore it's probably a very slow leak
-What causes the MC to fail repeatedly like that??

I will now order a new MC. I found new/reman boosters on ebay, but they are the small diameter, long type and I have the large diameter, short type (003 430 42 30). My only option with the current booster is to get it rebuild. Could I use a booster from a W202? I think I can get a reman or new one.

I used Centric brand MC's both times. The first time it broke I tought i got a defective part, but now it would be one hell of a coincidence. What could cause my MC to fail 3 times in a row like that? It's like the engine is pulling too much vacuum and blowing the seal.