I can say from personal experience that cylinder head bolts CAN work loose. Especially if the engine was recently rebuit and the bolts not torqued properly. Even if they were, I make it a practice to re-torque head bolts after the first few hours of runtime.
Follow Busted Warrior's advice and re-torque them. It is not too difficult to do once you remove the fuel tank and seat.
If the bolts are torqued to spec and you still have a leak, you will need to pull the head and have a look. There are two, smaller Allen bolts on the left side of the engine which will have to be removed in order to get the top end off. Even if the engine runs great and doesn't smoke, there is an internal oil return passage built into the top end on the Warrior engine. This passage is sealed with two 'O' rings, one on each end of the jug. Chances are that at least one O ring is pinched, mis-aligned, or dried-out, causing your leak. Remove the head, then the jug, and inspect all O rings. There is also a large O ring around the bottom of the cylinder, which works in conjunction with the base gasket to seal the top end. Check this one, too.
Basically, tear it down, check it out, get a Cometic top end gasket set and install it, then reassemble/torque the top end back to spec. Sorry for the rant, but I've done this exact procedure before and know what a headache it can be. Good Luck!
