I've been riding around for a year already with 2 stripped valve cover bolts with a little leakage but now its becoming a problem. Can someone tell me what size helicoil will work? Do I have to use the helicoil or can I use a knockoff brand?

 

Helicoil is a knock-off brand... what you should be using is a TimeSert. The size is 6mm x 1.00 pitch.