In the past couple of days, somewhat more than the usual amount of water required to top off the chiller has been added. This morning I added ~200 ml. Yesterday JeffB added a similar amount. I took a look under where the air trap was installed last week and sure enough there are some drops hanging onto the pipes and a wet spot on the floor underneath.
Found a leak between the 1/2" close nipple and the ball valve. Leak was not apparent when first installed because there was, by design, a trapped volume of air in the standpipe. After this air vented, the water leaked next. Tightening the connection between the valve and the close nipple slowed but did not stop the leak. Will replace the ball valve and the close nipple tomorrow morning, which will require the laser be shutdown.