panic propane isn't dry it just doesn't wash oil away lke gasoline does,that is why your cylinders and rings last so much better.now as for exhaust valves they microscopically weld to the seat and erode it away because of no carbon to pad them. Seats are an easy fix, needed with no-lead too ! heads with induction hardened seats will work,but once ground are susceptible too ! most of the 235 heads I see have the guides knurled,and seats are deep , new guides,hard seats and hard button valves will give these heads a new life. I give them a 3 angle seat with about a .060 seat width ground at 46 degrees with a 45 degree valve.
