The first thing I did was call GPI, who manufactured my pump. To save you the time, here's the phone number:
Great Plains Customer Support: 800-835-0113 or 316-686-7361
They told me they did indeed have a problem with gears being the wrong plastic; the changing formulations in fuels caught them by surprise, and they had a rebuild kit they would send me for free, since our pump was still in warranty.
If yours is out of warranty, or, you'd like to really confirm that the gears are the problem, here's the procedure.
After measuring the gear thickness, get a new sheet of 220 grit sand paper. Place it on a flat surface.
"Grinding the gears", ha ha
Using a figure eight pattern, sand the gear down on both sides. Using any other pattern, such as side-to-side, or circular, will result in in a profile that is not flat.
At the time, I didn't have the new gears, so I went to 0.748". It worked fine
Re-assembly (see below) with these sanded gears will confirm that the problem was swollen plastic.
After three days, the new gears arrived from GPI.
The new gears - somewhat over-packed.
Old (L) and New (R). The kit comes with a new drive bar, don't lose it!
After cleaning out the gearcase, I found that replacing the driven pump gear first made it much easier.
The drive gear, with the drive bar slid in place
After placing the drive gear, it is easy to place the second gear.
Inspect the o-ring, and slide the gear cover into place. The manufacturer says to use 90 to 100 inches of torque.
The steel bolts are easy to strip the aluminum case, be careful...!
From here, I left the pump unsecured. Then, I turned on the battery to test the pump.
Made sure the pump switch was in the off position
To avoid damage, this switch should be OFF unless you're actually pumping fuel
And finally, turned on the timer.
LED is lit - ready to test the rebuilt pump
From here, I went back to the fuel station, and turned on the switch. Voila! The pump whirred reassuringly, and I was able to dispense several gallons to test the pump.
After dispensing several gallons, I let the pump rest for several minutes, then checked for leaks. There being none, I re-secured the pump assembly.