I wonder about the procedure for replacing the packing. I would assume that once the boat is run for a bit, the packing will "settle in" and the nut will need to be tightened again? Kind of like when installing headers on a car: after installing them, the heat cycle can loosen the bolts a bit and after like 50 miles, they need to be tighened again. I am not sure, as I have never replaced my packing (560 hours on the original and only tigthened the nut once) but it it is just a theory.
I had the same problem two years ago and it was two things my center bag was filling continously and overflowing into my bilge fixed that problem with a new orbit valve and it was still leaking pretty bad so what i found was where my wake plate was mounted one of the screws coming through the floor was leaking really bad mainly when the boat was underway and just barely when sitting still. My fix was got some 3m 4200 and put on the threads of the screws ran them back through then put some on the inside where the screw came through also. Same model and year as yours also.
your packing SHOULD have a "drip rate" according to specs. My 2K Mobius has a drip rate for the packing of 1 drop every 30 sec. to 1 minute. I don't think you need completely STOP it. At least that's a MUST for my boat. Good luck.
Have either of you (or anyone else) replaced these valves with the Irritrol 700 series, or have a walkthrough for it? This may be my problem as well.