To follow-up on the leak check yesterday (which showed a slow leak), I repeated this test today:
1033 P=1004.88 (pinched off)
1034 unpinched Pref (so I could read pressure easily) P=1007.29
1037 installed tee, P=1007.32
1038 blew in, P= 1029 dropping
1039 pinched entire array, P=1025 still dropping
1041 tighten tee, P=1021.5 still dropping
1043 pinched off 11b P=1018.9, still dropping
~1100-1113 reseated both reservoir endcaps with more Teflon tape and plumbers' grease. Was able to screw in at least 3 whole turns more (due to grease lubrication)., P=1007.29 (had been open to outside)
1114 blow in, P=1048.3, dropping slowly
1117 P=1046.9, dropping slowly
1119 open 11b, P=1046.6, no obvious change in rate of dropping
1120 open entire array, P=1046.3, again no obvious change
1127 disconnect tee
1129 back to normal, P=1007.27
1134 backfill hole (again!) P=1007.6
Conclusion: reservoir had leak with 10min constant due to not-completely-seated endcaps. They are now seated better, with a much smaller leak (though the decrease in P could have been moderated by a change in temperature, that should have increased P).
We still have the wind correlation to investigate...