94 SL600 brake issue
 

I have a 94 SL600 that spends alot of time in the garage and short trips. Today after twenty minutes on the road the brakes started getting soft and eventually the pedal was hitting the floor. No brake light came on and I had to pump the pedal to get it stopped. I was limping it home and about 10 minutes later the brakes started working normally. Took it out where I could check it and did some hard braking and everything worked great. No fluid leaks or detectable vacuum leaks. I am hoping someone out there can steer me in the right direction before I start replacing unnecessary parts.