Below is stolen from ENH. A word of waring is this concotion will degrade bushings and rubber gaskets/o-rings but appears to work quite a bit better than PB...
Just figured I would share my experience with a home brew penetrating oil I learned about on the web. Long story short I have a very stubborn body mount bolt on my jeep that needs to come out. I tried everything I had in the garage...wd40, pb plaster, 'free' by some commercial company, even tried heating the capture plate to expand it and squirted some fluid film on it. Nothing worked. So while trying to figure out a way to get this bolt out I came across a formula for a diy penetrating oil. A 50 50 mix of atf and acetone. Put some in a spray bottle and squirted some on the bolt and waited about 15 minutes. After a little back and forth action with a wrench, much to my surprise, the bolt actually started to move! I resprayed the bolt again in hopes that more of the mix will work down the bolt and I'll be able to buzz the bolt out with my electric impact. I'll report back with my findings. Just figured living up here in the rust belt, every little trick up your sleeve to get rusted stuff loose helps!