Cregan

I was wondering if anyone had any ideas. The last cylinder was replaced due to no compression. We replaced the entire lower end. less than 20 hours on new cylinder the third cylinder is shot again. I did not trust the oil injection, so I was even mixing oi in the gas to make sure i wasnt starving the cylinder and it is bone dry again. One guy said it could be a bent shaft? Does anyone have any suggestions. I am not sure it is even worth dumping more money into.
Thanks in advance for your help.