Leaking twine pump JD 530

I have been running a JD 530 baler for several years and have noticed a leaking twine pump for awhile.  I have been able to add fluid to it to keep it going with the intent to replace it someday.  I went to bale Sunday for the first time this year and the pump was empty and I ended up having to prime it with a little air pressure (poor wife got covered in fluid  ) and she says it's time to replace the pump! Ag-Pro wants $440 right now for a new one and I really don't want to buy a rebuilt.  I have read about some others using a GM power steering pump as a replacement  - has anyone have any information and experience with that?

Leaking twine pump JD 530