Last week my truck started to leak brake fluid from under the driver side behind the master cylinder, brake booster assembly. so i thought it was my Mcylinder was bad,i changed it out,bled the system of air. the problem was still there, so next i changed out the brake booster still nothing. i read somewhere it could be a propostioner valve, so i went to my local pick and pull salvage yard to see what i could on some trucks that where taken apart, i found nothing. so i when't back home and jacked up the front of my truck took the driver side wheel off took off the fender well partition and this is what i found. between the frame and body of the truck was an old repair, a compression fitting that had a hole warn through the top of the fitting. i repaired the brake line,and all is good once again?

 

Wow, looks like it was too tight against the frame.Probably took awhile to wear a hole. It shows the problem is not always the obvious. Thanks for sharing