Best Penetrant to Remove Differential U-Bolts?

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.
My buddy had me pick up a bottle for him at a local aircraft supply place that was on my way home. Chief Aircraft. Think they do mail order. I remember it was pricey.