Second owner of a 450D, currently replacing the undercarriage. Everything has gone well except the piston for the track tension assemble, they are badly pitted and most of the chromed end is not usable. I would like to replace both of them, one side came off with some work. It was very damaged on the end close to the spring and did not appear to be sitting well in the cup. The other side is the real problem. It is rusted really bad into the cup, I would like to just torch it off and use the John Deere special bolt T16678 to remove the spring, inspect cup and replace piston. I am having a difficult time finding the spring compression bolt mentioned above. Does anyone know what the thread is for that special bolt is? Also does anyone have an aftermarket part for the piston. My local JD dealer in Kalamazoo seems reluctant to help, so and advice would be appreciated.