The o-rings should be lubricated with O-ring lube, not glued or sealed in any way. An o-ring cannot function as designed if it is held by sealant. If the covers are warped or compromised in any way you can use Yamabond or other similar sealant to make it leak proof. Otherwise I have always used 574 with zero leak problems from the covers.
The real reason they leak is too much crankcase pressure from worn cylinders, poor ring seal or removing the hose from the intake to the oil separator that provides slight negative pressure. Greg F