I just had calipers go out on both my 89 300se and my 90 420sel over the Christmas holiday. My 300se just started puddling in the garage and was leaking slowly. My 420's brakes was working fine one time and I got back in to drive back home and the brakes were very spongy and almost not there. I check the tank and it was almost all gone. I made it home and then the next day took it to my mechanic and sur enough the caliper on the passenger front wheel was bad. I had it replaced and it ran me about $150 with an excellent condition used caliper. I had the 300se replaced, but the fluid had soaked the pads enough that I had to put new pads and while there the mechanic noticed that the rear rotors (where the caliper was bad) were under the specs for replacement so I had them replaced as well. That job ran me about $350 total. I understand that calipers are a weak spot in these cars once they age a little bit. I would bet 99% chance it is one of your calipers. Check the inside of the wheels and you can tell if fluid is leaking out and running down. Good luck in the repair.