This old '82 6.2 has been sitting for several years outside, under the hood of a Suburban. The compression is equal on all cyls at about 120 PSI. I pulled it and have it on a stand, and have shot some Marvel Mystery oil into the glow plug holes because I think the rings have set up. What else could it be? The guy I got it from said it was low miles and ran fine before. Right now I am on my 2nd soak with MM oil. 1. Is there a better oil to squirt in to unseize rings? The 2 syringes in the photo are "flavor injectors" I found at supermarket. 30 ml capacity with graduations. Perfect for knowing how much oil you have put in. 2. how long should I let the MM oil (or something else??) sit in there? The first time I let plain 30 weight sit sit for only a few hours. This did not improve PSI. 3. what should the cranking RPM be to get a proper PSI reading? I tested with glow plugs out. Oil I added, squirted out all over the place from the glow plug holes.