My son sold his 380 sl with the dual chain cam heads. It was VERY VERY rapid, but the newer motor made it difficult to sell.
PB Blaster comes in a white base spray can, and the better paers stores carry it along side Rust Buster, Liquid Wrench, etal. PB works best by spray-tap-let sit 10-15 mon, spray tap , let sit, spray tap try and remove. It has a CHEMICAL reraction between oxidation and the good metal and breaks the bond.
BTW, years ago I tested Marvel Magic Mystery Oil in an experiment of my own design, and found that it indeed has a positive, measurable effect. One that is worth, in my opinion, the price of the product.