If you have the Wilcox & Crittenden Headmate Jr, it's not worth repairing. They have been discontinued for some time now, and rebuild kits are becomming scarce and costly. In addition, the pump body is probably worn, so rebuild kits give a less than satisfactory result, and replacement pumps are even scarcer and more costly.
Your best bet is to replace it with a Raritan PHII compact. The PHIIC pump has twice the volume per stroke than the WC Headmate, is stronger built, and parts are available everywhere.
I went through this same dilemma a few years back. The Raritan is pricy, but better to cry once and get it over with. Having to deal with a malfunctioning head during an extended cruise while living on the boat is no fun! (Don't ask me how I know this...) Its amazing that my wife still wants to cruise after having to use a bucket for a week!
The PHIIC will just fit in the P323's head area, and with the telescoping pump handle retracted, the bifold door can fold past it. This does require mounting it slightly to the left of where the Headmate was, but it has worked out perfectly for us.