Ford A/C :: Draining The Compressor Oil?

I have a truck, info is in my sig, and the A/C system has lost it's charge. I haven't had the truck too long and don't know how long it's been since it's been ran. I have a little background in A/C and refrigerants so I just have a couple of questions. Since this system leaked down to atmospheric pressure, how do I go about removing the oil from the compressor? I might have to remove the compressor but was trying to avoid it. I can if I need to. I know that it's R134a and it uses POE oil that is azeotrophic so you can't remove all the water and the remaining water will turn to sludge and acid. I know that I should probably change the drier and all the o-rings, but is there anything else that would need to be changed?

I know that the pressure switches are good, or at least the low pressure, because when I put some refrigerant in my girlfriends car because of a leak, I put the rest in my system to see if I could get the system to turn on and cycle. It did and I shut it off. The system was at 0 psig when I put the gauge on it and it took about 3 weeks for it to complete leak back down to 0. The compressor sounded good so I would think that it would just be a small leak. I think that the low pressure switch saved the compressor when it was low on charge. Am I overlooking anything? I have a manifold set and a good vac pump. I think I can just charge it back up to factory charge after I fix the leak and go from there.