But, @
humfrz, what if it's not a leak? The AC suddenly died in Mrs. Ultra's Camry. It ended up just being a clutch relay.
Especially since this system doesn't come with a sight gauge, I advise against adding anything unless:
1. Coolant loss is certain
2. The leak has been repaired.
Also, I've read warnings about incompatible formulations of lubricants and additives. Make sure you're using the right stuff.
Not an expert but my $0.02 nonetheless.