I forced myself to do a reseal pump job with a video a guy on ebay sells and am glad I did. If you have the time and tools and what to save money and reseal a working pump its a great option.
Now every engine I put into a service I do a complete timing belt/water pump job and yank the pump off the car. Because I have now been bit more than once by replacing an external seal while on the car and have another leak shortly thereafter.
Seeing a diesel leak on these cars makes my heart sink and after seeing the kind of mess it can make on new coolant hoses I refuse to ever go through that again.
Plus when you have the pumps apart you may not notice it on a running car, but the vane cavity can be gooey effecting the pumping.
A vise and the ability to work with your hands and potentially make tools is what you need.
Job is easy, I originally worked on a spare junk cheap pump I got just in case I screwed something up.
What I do is externally clean the pumps before starting and mark some pivotal pieces with a swab of nail polish so you can get the orientation correct. also a picture of a few areas is a good back up. its just not worth tearing into it without doing so and trying to remember.
Doing it this way I can't say I have screwed anything up on running used pumps. Thats a handfull now that serve as daily drivers still in service.