1. Its the piece from a compression tester, instead of putting the compression gauge on it you hook the air hose from your compressor to it. Autozone rents the comression tester if you need one.
2. ^^^^
3. Why oem? Why not vitton? seals just slide right off and when putting the new ones on I used a socket upside down and slid it over the valve to seat it evenly. The valves won't fall unless you loose air pressure in the cylinder