Generally no system oil is removed when evac'ed,only when components are replaced(evap,condensor,receiver/dryer,and compressor).Must use PAG oil and generally add specific amounts to each component,you add tracer dye through the low side port.
Agreed. Also, if you pop the hood, the sticker on the radiator crossbrace lists not only the type and amount of freon for a full charge in the system, it also lists the type and amount of oil needed as well, depending on which type compressor you have - there's two listed on the sticker on my 05 CRD, the first one is for gassers, the second one (which has a part number something like PDX-***) is for CRD's.
From what I understand, on older vehicles that have had their R-12 systems converted over to R-134, you still need to use Ester oil with the R-134, as PAG oil will seep thru and degrade the original hoses that were designed for a R-12/Ester combination.
On my first used 87 MB 300D that I bought in 06, there was a sticker under the hood where the system had been shop converted over to R-134, listing the amount of freon, and that they'd used Ester oil and that amount as well. Those beasts have large A/C systems on them - original R-12 charge listed in the MB FSM is 1.1 kilograms - close to 2 1/2 lbs. Even converted over to R-134, that system was idling with the blower at half-speed to keep that car cool on a 103 F Texas day with 50 F air out of the vents.