Ty, some kinds of varnish can be a real problem that should not be ignored. (Warning: anecdote content coming.) Way back before the 1950s, racing engines were always lubricated with castor oil because mineral oils did not have the required additives to make them work properly under extreme conditions. This presented many challenges which I won't go into, but one that was important was that very hot castor oil formed a varnish when it cooled. The varnish formed in the hottest places, including the big end bearing surfaces. It could not be removed with conventional petrochemical solvents. In general it was not important, because it was dissolved by hot castor oil, so you could keep using the engine. Unfortunately, if you switched the engine to mineral oil, the next time you ran it hard, the varnish would partly melt, fail to mix with the mineral oil, and cause a seizure - usually at high speed. There won't be anyone else here old enough to remember an event at the Sandown car racing course in I guess the 1980s when people dragged out their collectible racing cars for exhibition runs/pseudo-races. There was some really fine machinery there that day. Unfortunately a well known rally identity borrowed a Maserati 300S (1956 sports-racer, a very notable classic racing car) from Bob Jane's collection, and ran it as hard as it would go. The result was a broken connecting rod and a large hole in the side of the aluminium crankcase, and the forensic analysis found the castor oil varnish on a big end bearing was the cause. Much bad blood ensued when the rally identity refused to pay all or part of the repair cost.
I think you need to pull it down and remove any varnish that has found its way inside the engine, Ty.
