Everyone loves to reach for the WD-40 when a penetrating oil is called for. But did you know that you can cheaply and easily make your own? There are dozens of recipes out there (do a YouTube search). Here are two that get high marks from many basement penetrant chemists:
Recipe 1: 4 parts charcoal lighter fluid, 4 parts mineral spirits (or paint thinner), 1 part lightweight motor oil.
Recipe 2: A 50/50 mix of acetone and transmission fluid.