I just noticed a tiny piece of black tape under my master cylinder today, so i took it off, but when i started up my truck i heard a hissing noise, kind of like a vacuum leak, and sure enough there was a tiny hole that the tape was covering up, maybe 1/8" in diameter, undernieth the master cylinder at the back, by the brake booster. Does anyone know what that is for? Can i just plug it? Ive been driving it for years and years and i dont remember putting the tape over the hole. everything seemed fine.