451 509 mopar cam, hd stamped rockers,lifters from two different sources do to rust on Mopar lifters....13 Mopar lifters...3 sealed power.

Engine has bout 3 hours on it and the pass side rear has a honest to goodness loose rocker sound but you pull the cover and theres no lash and the lifters are all pumped up and hard.Springs look ok.Havnt removed the rocker rail yet am kinda stumped.A friend says i might have got a anti pump up lifter in the mix but really see what that would do??Or he thinks the valve seat might not be right i just dont know.

Whay ya think?????Thanks