Hey Scotthewolf, I just saw this posted, I don't log on all the time but noticed this post. The actual fix for this is rather simple and complex at the same time.
I've probably seen this over 30-40 times now and repaired them all. The problem is the evaporator fan motor kicking on too quickly and spraying moisture
to the upper damper and slowly clogging it. Also the bypass duct by the vegi-crisper will ice up because air cannot flow through the upper damper freely.
The fix for this is to use the air scoop heater #483166, and attach it to the back of the plastic cover in the upper freezer. Then, after clearing out all the ice
from the damper and the by-pass duct, install a fzzr thermostat, in-line, on one leg of the evaporator motor. This is to delay the start of the fan from blowing up the moisture and letting it settle down before starting up again. Also, tell your customer to keep food away from the by-pass duct at least 4 inches so air can flow more freely. You will notice that once this is done and plugged back in, the refrigerator will not start until the by-pass thermo you install closes and kicks in. This will take another 15-20 mins or so before the fridge acturally starts up. Its a good idea to inform your customer about this so they know that it will eventually start up and not panic. If the fan starts up right away, then you have installed it incorrectly. The fan must always have a delayed start. Good Job you doing by the way. I've learned a lot from you.