Thought I cured this by modding the cover bolts so that the covers don't sit as high up on the top rail and using a wider style gasket. Well it didn't last very long. Seems to be just the RH side that is the problem. Both covers are vented to a breather tank. Blew out in the same place last time. I don't think it is pressure related or the push in oil fill cap would pop out 1st. Any ideas?

edit: Just took a closer look and it looks to me like the cover has moved upward again so that the gasket was only half on the top rail. Either these covers don't center well on my ETP heads and/or the Crower SS shaft mount rockers are bumping it up. I did notice a couple of marks on the inside of the cover before and clearanced those areas.

 

Don't think there are any new marks. Looks like the top rail on the head may have been narrowed to clear the rockers.