I have broken two rocker studs in two weeks. I have a 306 with 351w heads, harland sharp roller rockers and a f303 cam. The studs are 3/8 base with 7/16 adjustable nut. The two studs both broke off in the adjustable nut. I'm going to replace all the studs as a first priority with ARP chromemoly studs. The breaks look like bad constuction of the studs. No damage to the rockers and the pushrods are not bent. Any other ideas why I might be breaking rocker studs???