Best Penetrant to Remove Differential U-Bolts?

Aircraft mechanic buddy swears by this. Won't use anything else. IDK.
Airplane price so it's probably cheaper to buy new u bolts, lol.
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Years ago I had a neighbor that was a machinest at a local AFB and he gave me what he had left of some Mouse' Milk. This stuff worked equally as well. I used up what was left and couldn't locate this stuff on the open market. That was over 30yrs ago, nice to see that its still available. Well worth the money. Plus it doesn't smell like many of today's solvents do.