im leaking fuel around petcock on/off knob when i turn it to on i can see it dripping .... any one know how to fix it
Rebuilding it is the most cost effective option. That is if you are comfortable taking it apart and putting it back together. I would purchase both of these and in the meantime, switch the valve to the OFF position when not in useThere are two o-rings for the fuel tap assembly. One is behind the switch (part 92055-1419) and one is between the assembly and tank (part 92055-1112)
The parts are cheap and taking the fuel tap off is fairly easy. If your sure that something in the fuel tap is leaking just reubild it.
And while your at it, consider Ninja92's advice. The fuel lines rot pretty easily especially if the bike has been sitting for a while.