Well, I'm concerned with underfilling it too. Seeing as the pump is the lowest part of the system, is there any accurate way to drain and refill it in situ? What's the total capacity in a new system?
Also, what about the corrosion in the condensor connector? Any need to be concerned? It's not throughout the system, but I don't really know how far it goes, only that all the other hose and pipe connections looked clean internally. Is a little bit of corrosion normal over the years and does it tend to stay put?