What you should do is to break all lines and flush the complete system to remove the old oil. THEN you can put the correct amount of synthetic, distributed among the components. You then have a clean system with the KNOWN correct volume of oil in place.

BTW, I would be hesitant to use the Scuba shop oil. Reactions with unknown substances within a closed refrigeration system can sometimes create acids that will eat up components from the inside out. There is an inexpensive product called Nylog that is specifically designed for assembly of O-rings in refrigeration systems.