Could be your breathers are plugged. That happened to my freewheeler

 

 

No too much oil would not cause that.
Those gaskets/seals are a very common leak point, you can try torquing the bolts to spec but it's probably time for new gaskets

 

 

Harley has improved their top end gaskets and I like them better than cometic gaskets. I've used OEM the last two times I've installed Hammer kits and not a smidgen of oil leak.

 

You're not in the Sportster club until you have to replace a rocker cover gasket.

 

 

I used the Cometic gasket kit and it has been holding up for over a year. They make solid products.

 

Having used all of those and more, I can say that the answer is: it depends.

I've had poor gaskets from all, and I've had great gaskets from all. A cometic MLS gasket is not always the answer compared to an HD one. Overall, they're all good and I would not hesitate to buy any of them. I tend to favor Cometic for almost everything, but there are a few rare cases where I use James because Cometic just hasn't quite gotten that specific gasket right.

For late model bikes, HD's gaskets are quite good. Leaps and bounds past their own gaskets just a decade ago.

And when in doubt, I've got a roll of Felpro gasket material (.030"/1/32", I know that's not directly converted, but close enough) that I cut to fit those special ones.