This is why I pretty much stopped fooling with flat tappets. I put one in my dad's car this summer.I bought a case of comp cams break in oil. what he runs in it.
He rarely drives it so he just uses that since it is loaded with zinc. I still don't know if that's a good idea or not. Anyway, I have never had one go flat and I used to run them...and I never broke them in properly either.I Just started it up, set the timing and idle etc and forgot about it. zero problems.
Now after reading online the last few years about the problems that people smarter than me have, I'm afraid to mess with them...I just run solid roller in my race car and a hyd roller in my chevelle.