I don't know if any commercial outfit does it, but you can purchase individual parts for everything & get them from Mercruiserparts.com. I't sot of difficult to find the parts breakdown as it is not in the regular sections. You must look under some of the performance areas at the bottom of the list. I fixed several leaks in my pumps with parts ordered (new o-rings, screws, etc) They worked perfectly. Easy to do but a little messy.
Hydraulics really aren't that difficult unless you have to design a system. I'm sire many o-rings & seals could be purchased at a local hydraulics shop also cheaper, too. Many pumps are on ebay, but all at $200.00. O-rings are far cheaper!