I have a 1940s approximately farmall cub. I checked the compression in cylinders 3 and 4 and got about 25 I think. I took the valve cover off the side and thought at first everything looked ok. I then looked closer later and realized 3 of the exhaust valves are stuck open. I took the head off and have tried using pb blaster. I got them to move but I have to hammer them pretty hard to get them closed. They are FAR from closing on their own. I don t know if I should keep trying to beat them loose or just replace them. I have considered putting pistons and rings in it as well considering I have tore down this far and the fact that I don t know for sure that the rings are good. Any help as what I should do is appreciated.