Tips on valve cover gaskets, these techniques worked for me:
1. Replace the 2 grommets too, they get compressed with age, replacing them ensures the cover is pulled down properly.
2. The gasket fits tightly in the groove in the cover it can be difficult to get it level. If you put some petroleum jelly in the groove of the cover using a epoxy brush, it's easier to install it level, and the petroleum jelly will melt away once the engines hot.
3. Put a dab of Permatex RTV grey or black, in the 2 corners of the gasket where the half-circle meets the straight run, this seals up the sharp edges at the 2 points on the cylinder head notch.
4. To avoid knocking the gasket out of place, rotate the crankshaft until the front exhaust valves are fully open. You can rotate the engine without removing the left crankcase cover plug, with the bike on the center stand, put the transmission in 5th gear, and bump the back wheel.