Had mine rebuild a few years ago , 400E , not at a porsche dealer or porsche specialist , just a regular shop rebuilding powerstearing equipment , ac pumps etc , all brands place .
Came with warranty , had a smal leak and when cold a intermittend hickup not working for less than a second .
They took it appart when i deliverd the rack , took him 5 min or so , he wanted to inspect a few parts , to let me know if he was able to repair the rack , it was within limits , so left it there , and picked it up next day rebuild , new paint on it looking and working as new .
I could have done it my self looking at it , but no way to test it before puting it back in the car , wich they do , came with the test report .
I would look for a specialist in powerstearing equimpment , the parts where not hard to get he said , most off it standard o-rings etc