Hi!
Been racing for 36 years and have never seen an engine with old castor congealed bearings clean itself with any liquid, be it aceton,methanol or heat.
The only certain solutiion when a bearings is old and worn and feels gritty is to replace it with a new bearing.
I have seen engines where the crankshaft spins freely and when the engine is taken apart the rear bearing is so rusty and full of orange congealed castor oil that the crank spinns on the inner bearin surface and the rest of the bearing is stuck.
Ofcourse the engine works...but how well? And for how long time?

If you are serious about your engines, take the engine apart and replace the rear bearing! It's so easy to do!