I would be curious why they are breaking. There is no load on that part. If there is than your cam is going downhill in the block. I wouldnt say there is a problem until it happens to someone else. I am trying to figure out from that picture what kind of block that is, we have to machine the iron boss around the cam to clear the cover, even on the older blocks. That one has no boss. Its irrelevant, I am just looking for clues. I would say that Gary seems to have a run of bad luck, he handed me a coffe can full of broken valvetrain parts at vegas, and said the valve was bad. I looked at it, the spring was broke, and by the looks of the stem it had been broken for a while. No valve will live under those conditions. These cars are not wind up toys, you have to A)look at everything, and B) know what you are looking for, which most dont.
cw