My bike had that very same bolt stripped when I got it. I ignored it for a long time.
It would occasionally leak around that area. I finally got around to fixing that one and a couple others that were close to being gone. I used Helicoils (Size = M6), bought a set that had everything you need and a handful of the coils off of Amazon for about $24. It was easy to do too. Came with instructions. You will need a 1/4" drill bit too, kit doesn't come with that.
It currently lists for $25.31
http://www.amazon.com/Helicoil-5546-6-Thread-Repair-Kit/dp/B0002KKPXK/ref=pd_...