As you know, there is the R134a refrigerant cans available as well as the R134a oil for the compressor. First of all, how much will your A/C system take (one can or two cans or R134a refrigerant)? Secondly, what about the A/C oil for the compressor? How much oil are you supposed to add?

Do some light reading ;)

http://www.pelicanparts.com/bmw/techarticles/101-Projects-97-AC/101-Projects-97-AC.htm

Good article. As for the oil, I've had a hard time finding an exact answer as to how much oil you add. Most shops either quote the total oil amount specified by the manual, or they say that when you remove a component (say, a condenser or a compressor), you pour the oil out, measure the amount you took out, and add that amount.

To my knowlegde, a refrigerant leak shouldn't leak out the lubricating oil, but I may be wrong about that.