JD 52D Auto Connect U-joint Failures

I have a JD 1025R with a 52D auto connect mower deck. I have had three failures with the u-joint that is on the pto power drive assembly. In each instance the u-joint literally breaks apart at the quick connect position where the power comes out of the front of the rear axel. Has anyone else had this problem and how did you resolve it? Additional note: about half of the time when the pto switch is selected to on, a loud clunk is heard as the mower starts. The rest of the time when selecting the pro switch to on, it is nice and smooth. Could this be the problem?