I replaced the compressor in my '82 380SL about a month ago, and the instructions that came with the new compressor said to pour the entire amount of new oil into the low pressure side of the compressor, then position the compressor so that the nose of the compressor is pointed down and leave it that way for at least 15 min. to ensure that oil gets to the shaft seal, then turn the input shaft at least 15 turns, then install the compressor.
This info is right off the four seasons instructions. Not trying to dispute anyone's instructions here, just providing the manufacturer's instructions. Keep in mind that this is for the older style compressor, and may not apply to the newer style ones.

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Richard Wooldridge
'01 ML320
'82 300D 4.3L V6/T700R4 conversion
'82 380SL, '86 560SL engine/trans. installed
'79 450SL, digital servo update
'75 280C