See if you can find a can of Aero Kroil. It comes in an orange can. Its some of the best out there. I've used it with great success. The manufacture is Kano Laboratories in Nashville, Tn. They may have a web site Im not sure. I had a frozen 12 year old o2 sensor I sprayed and let sit overnight, and you could almost have loosened it by hand.
Its industrial grade stuff that reduces the surface tension so that the solvent creeps into openings as small as one millionth of an inch. Good luck.
1989 420SEL 105575 miles
1990 Chevrolet E-Cab C-1500
1989 Olds Toranado Trofeo'