Just got back from first long trip with the truck 95 1500 4x4 5.9. The front of my master cylinder reservoir is wet. It looks like the fluid leaked out from the cover. Cover was seated properly and the fluid level correct. What could be the causing this?

 

Front reservoir is for the rear brakes, I think.... are your rears adjusted to tight? Might be boiling the fluid, and blowing it out......

 

The rear brakes are adjusted. Could something cause my MC to supply pressure to the reservoir( vent to tank?). Its a new MC. Brakes are working fine with a bit of travel at the pedal.

 

Nothing in the system, aside from the pedal.... will build pressure. Did you fill it up recently? (given its new... I am going to guess that is a 'yes'...) Its possible that it was just a bit over-full, and when you step on the pedal, it actually displaces a bit of fluid back into the reservoir, before applying pressure to the brakes.

Recheck fluid level, clean everything up, and see if it happens again.