I had a leak around a cylinder sleeve and tried a couple things that worked only temporarily. Then I came across this stuff that was guarantied to work or double the money back. I decided it was worth a try. It was kind of expensive but it did work and has been working for about three years now with no signs of failure. This is very good because it is in a numbers matching 428CJ engine and I would rather not have to re-sleeve or replace the engine.
The product is K&W Nanotechnology Head Gasket & Block Repair. You have to follow the instructions exactly which includes draining the block completely. I went an additional step and pulled vacuum on the cylinder that was leaking after running the engine the prescribed time. I can't guarantee that it will work but the manufacture does.
2002 FX4 Bright Red Supercab 4.0 SOHC, manual 5-spd & Tcase, 33" BFG MTs, K&N air filter, Modified air box inlet, Gibson SS cat. back exhaust, Bama flash, Hidden Hitch round receiver, Rear helper air springs, Electric trailer brake controller, Line-X bed liner, WAAG bar with KC lights and Wildernest shell.