Those aluminum hold downs wear out really quickly if you don't have a hardened shim between the rocker arm and the hold down. I learned that lesson once myself!

Low buck setup is to just put some hard shims in there. You should also have hard shims on the other side of the rocker arms between the spring and the rocker. Total cost for that upgrade is just a few bucks for a pack of shims.

Better upgrade is to put the nice steel hold downs on there that Hughes sells. Even with the steel hold downs you should use a hard shim on each side of the rocker arm.