Buy the kits, take it apart on a clean workbench and lay it out the way it comes apart. Clean the parts in degreaser. Line up the new with the old, apply lube to the rubber and seals, replace all the bits. Most kits have clear instrcutions.
Unfortuantely there is no one kit I have found that has "everything". Need to but the seals for the valve, the ball stud, and the seats separately.
If your mechanic needs instructions I'd find someone else or DIY, as if they don't know how to do it you can do it about as easliy following the instrucitons and just looking at how it comes apart and reverse the process to put it back together.
The only real tricky part, that I found, was in unscrewing the cap to get the ball stud out. There is a hidden pin you need to push out to get it to unscrew. I'll see if I can find a photo in the records...