Dennis, I have read in trade publications that flat tappet (hyd.& solid) wear is mainly caused by the removal of zinc from the oils because it shortens the life of catalic converters and 02 sensors. Manufactures were behind this because of the warranty, this is also why they all went to roller cams in new cars. Not for less friction but because the cams were going flat.
Rotella was one of the last to retain zinc but not anymore, there is a code to look for I will try and find, and post it.
I can't count how many cams I have heard of going flat but it's a big problem.
I think if you want an hyd.lifter use a roller hyd. If you want a flat lifter use the ones with the small hole in the face I have very good luck with this style, the lifter rides on a cushion of oil pressure. But you still need to use ALL the proper break in procedures.
They say you can use GM (engine oil supplement) with your oil to replace the zinc.
