Last month, I found my 428 idling a bit rough, I did a compression test, and found number 8 cylinder very low, only 40 psi, compared to 185-195 for the other 7. Today I pulled the heads, and poured so solvent down all the ports, sure enough, on number 8, the solvent came pouring out of the exhaust valve. Removed that valve, and found the valve guide extremely sloppy, .150" of movement.I was talking to my machinist buddy, who has built dozens of FE engines over the years, including doing the machine work on several of my 428s, and he told me that over the past year or 2, the machine shop that he was 1/2 owner of, has stopped doing work on FE heads, he said that they have had several cases where they had similar valve guide issues, with valve stems galling and tearing up the guides. He said that they have only had this issue with factory FE heads, and has not been able to determine a cause. Just wondering if any other FE builders has been experiencing similar problems.