last week I bought a 2004 ZD28 with 1100 operating hours, in Germany. It has almost no power on the right wheel. I think it's the HST issue, described in this thread. I would like to learn more about your approach @davemskinner. Unfortunately, the pictures are not available anymore. Could you reupload them, please?
I will look for the pics but this was posted a long time ago. I'm not sure I have them.
Also, you should be aware the the repair did not last. I mowed 4 acres and the unit failed after about 8-10 mowings.
What was worse, was the failed pump sent filings throughout the system. I then had to replace both pumps/motors and completely flush out the charge pump.
My recommendation is to replace the bad pump ASAP before it blows apart AND thoroughly flush the system.
Update 8/11/22: I have searched all locations and cannot find the pics. So sorry. I will keep looking though and post if I find them.