Stovebolts seem to have a way of creating gummy residue crap all over the rocker arms, even with modern oil and good maintenance. I think it’s some chemical/physical outcome from the crankcase vapors.
You’re on the right track. While you have the rocker assembly apart, might want to inspect for wear of the shaft and the rocker tips. The aforementioned spinning of the oil pump with a drill is a good idea to verify a clear path for the oil. I’d probably do it both before and after reinstalling installing the rocker assembly. There’s a lot of weird, year to year, change in that oiling path. And it’s quite common for mismatched, incompatible parts to have been installed over the engine’s many decades of use.
Sludge and gummy films are likely present in other parts of your engine as well. Some here recommend a running “flush” by adding some diesel to overfill the crankcase and running several minutes at a high idle and no load. I have successfully done it, but I also know if freaks some people out. Ask more questions before you decide for yourself.
