AC vac results with question

[JimmyL]

I found a leaking high pressure schrader valve on my '85 wagon's AC system. Not sure if it is my only leak, as freon was desperately low. I resealed the connector with nylog on the threads and replaced the inner valve.
This was the only leak the sniffer detected at that time.
So, I then pulled a vac on the system for an hour, then closed the valves to check on it holding a vac. It moved from just short of 30 psi (whatever unit) to almost 29 1/4 in one hour and 20 minutes. (loss of maybe 1/2 to not quite 3/4)

Is this a substantial leak, or an inconvienent leak? (once a week vs once a season for example?)
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