Originally Posted by aspeed

Sometimes the finned heads warp a bit. It should be under warranty if they are still in business. It could be lapped out and carefully cleaned if it isn't too far off. Any scratch or dimple from a piece of dirt on the surfaces could leak. I sometimes use castor oil on the mating surfaces and found that it seals a bit better, other people find the opposite true. 400 sandpaper on a piece of glass and some careful twists can flatten the top of the liner before lapping the head.