OK, so my left petcock was leaking when I got the bike. 75 XS650B, manual (on/off) petcock, NOT VACUUM. Got a rebuild kit from Mikes XS, took it apart, polished every surface, put in all the new gaskets, put it back together, still leaking. One thing that got my attention is that the gasket on the back side from the kit was much thinner than the original, so I put the original back in. Still leaks. Decided to go old school and Permatexed it. Still leaks. Can't see exactly where it's coming from. It's on the back, not the outlet tube, not the on/off/res handle, and doesn't seem to be coming from where it bolts on to the tank. Can't tell for sure, but I didn't feel any fluid there when it put my finger on it. So it really seems to be coming from the plate on the back as far as I can tell, but with a new gasket, old gasket, Permatex, whatever, how can it still be leaking? I'll probably order a replacement from Mikes, but would love to have this solved in a shorter time frame. Any advice or sympathy appreciated.