I just did a set from my /7 ... If you have a 15mm bicycle wrench .. the kind that's made by a stamped out piece of sheet metal ... Like this:
You can use the pointed ends of the wrench to open the petcock ... really easy.
The rebuild kit contains three gaskets. The first is a circle with three holes in it. The next is an o-ring. These two are must's to be replaced and are both interior to the petcock. The third is a cork seal that seals the seal in between the petcock and the tank ... this one is difficult and I wound up making one that worked infinitely better out of an 1/8" rubber sheet (from a DIY gasket kit).
The first petcock took me ~15 minutes to do. The second one took me 2. Easy and no more leaks!!!