The best penetrating oil for stuff like that I’ve ever heard of was 50/50 acetone and trans fluid. I’ve mentioned that to many mechanics I’ve crossed paths with and some never heard of it but others agreed that it works great. Back when I fooled with motorcycles there was a 1 gallon can of carb cleaner that got everything loose. Left long enough it would eat the casings. Always removed all the funk we came across. Hope the casings are still good on yours. Good thing you like projects.m