81 300sd a/c compressor oil?

my system was serviced with freeze 12, would cool to about 49 degrees, 100+ outside, with some bubbles still in site glass. [as long as comp clutch was hot wired] then valve stem on high side started leaking and i lost all my refrigerant. [i replaced it] i was told the oil mixes with the gas and when you lose refrigerant you lose your oil. so now, my question is, how do i know how much oil i have left? how do i add more? what kind? [hopefully w/o taking off compressor] thanks gary