It has been a couple of years since I topped off my R12 in my 84 190E.
Before I put my manifold/gauges on, which was the HIGH pressure nipple, and which was the LOW side. If I recall the low was up near the left (drivers) strut tower and the high side nipple was over near the oil dipstick / exhaust manifold (right side)
(I know to fill on the low side!)
'84 190E 2.3
'83 Porsche 944 (track car)
'84 Porsche 944 (parts car)
85.5 Porsche 944 (sled)