Ive now had 2 Rs Cosworths being a 4x4 and a rwd and both have decided to Snap the exhaust cam at the rear 2nd cam cap from the back!

Can anyone tell me if this is common or why this happens ?

Am i guessing it could be the heat from the turbo/exhaust at the rear on that side or perhapes to many revs up to 6.5k ? and engine strain form pushing it hard ? (I have heard some miffs in the past about heat.)

This is a pic of the latest one that snapped but the other was in the dead same place.

Both Rs Cosworths were and are stage 3 est 350hp

Any help would be great please as dont want to do it again lol