I want to close this thread out by comparing the data sent to me by forum members.
I started this thread when I checked on the state of the sump of my stationary Mk3 and was surprised by 1 1/2 quarts of oil that streamed into and out of my 1 quart container. Since then, after topping off, I measured the sump flow over three days (results below). My mk 3 is a complete rebuild, but the oil pump WAS NOT refurbished as it looked good and passed the manual pump test (the bike has 24,000 original miles on it). I did refurb the check valve, which was, as many have stated, inoperable and stuck open. My measurement was made with the pistons at TDC.
Compiling the results:
Mexico Mike 1973 Commando refurbed pump no TDC 1.3 oz/day
PJL 1972 Commando 750 Combat no pump refurb at TDC 0.74 oz/day
Rick in Seattle 1975 Commando 850 Mk3 no pump refurb new check valve at TDC 0.96 oz/day
The manual reminds us to expect a "normal" sump oil volume of "a teacup or so" , say 8 oz? It appears from the remarkably consistent data above that this translates into 1-2 weeks of inactivity. Standing for a month, at least for the bikes above, would drain 1 quart (4 teacups?) into the sump. For myself, I plan to ignore wet sumping during the riding season as long as I fire up the Norton at least monthly. I'll drain the sump in the spring before that first delicious ride in the dry.