Best Penetrant to Remove Differential U-Bolts?

UPDATE:

Not scientific, but I experimented with the only two products I could find and purchase at Autozone, which was Liquid Wrench and PB Blaster. I used LW on the two ubolts on the passenger side and PB on the driver's side. After several applications I knew it was going to be a battle, so I waited overnight.

Using a not too long 1/2 drive Craftsman breaker bar, I was able to break the four passenger side nuts (LW) loose without too much difficulty. Once loose, I used the box end of a 3/4" combination wrench to spin them off. Of course, because of the self-locking construction, one cannot spin the loose nuts off by hand. I was pleased but still sure there was always a black sheep to be found during any such undertaking.

On the driver's side (PB), I was able to loosen two nuts with the same breaker bar, but obviously with more torque than was required on the other side. The other two nuts (on the inside ubolt) would not budge and I was afraid of splitting the 3/4" deep socket that I had borrowed. I gingerly put a pipe on the breaker bar a couple of times, but did not use full force because I felt too much resistance. I gave up on the oily, foamy PB and switched over to LW applications. (seemed watery and looked to evaporate compared to the PB). I went to lunch.

Back from lunch, still no luck so the shop owner went home to find something we could use to heat up the two stubborn nuts. While waiting for him, and after more applications of LW (and maximum effort that I dared try) I felt the breaker bar move slightly while at the same time I heard a loud squeak/squeal. I got less than a full turn on that nut, squealing with each movement, when I found I was able to slide the ubolt (and accompanying lower shock mount plate) over toward the carrier enough where I could remove the differential without even having to loosen the fourth and final frozen nut. Relief at last and already past 4:00 PM.