I don't have the seal info, sorry. The 480K tank is an odd one, because it has a valve in both ends. There are (as best I can figure) FIVE seals in them:
1 seal for the front fitting to the tank
1 seal for the rear fitting to the tank
1 valve seal in the front
1 valve seal in the rear
1 O-ring inside the rear tank fitting to seal against the "nose" of the threaded assembly on the pistol that fits into the back of the tank
This last one is a real pain to get at & remove without damaging something. All it takes is a small scratch in the wrong place, and you will have a permanent leak. A plastic hook could probably be made to fish it out safely.
As for tools, the rear takes a pin spanner. The holes appear to be 2.5mm in diameter, but they are spaced at 26mm center-to-center, which is a bit odd. I have no idea how to get the front valve out, you may have to do it from inside, which would definitely require a special tool.
McMaster Carr sells an adjustable spanner with 2.5mm pins:
http://www.mcmaster.com/#5501a27/=10t3its
The MIT team has at least a half a dozen 480K cylinders with leaks that Larry has refused to repair. If you'd like a couple to experiment on, PM me & I can see if the team will give them up for a small donation.