In addition to what was mentioned above, I broke 3 rocker arms and bent 3 or 4 pushrods on my 248 due to that old gas gumming up the valve stems.
I pulled the rocker assembly off and cleaned it up. Then using wd40 I ran a sledge down the row of valves, tapping and spraying, repeat, etc. It took awhile but all of them work fine now. Once that was done, I reassembled the rocker assembly and bumped the starter over slowly, so I could see if any valves still stuck.
Its slow work, but well worth the time.
Jeff
