Having too little preload on the bearings can absolutely cause premature wear on the axle seals.Man I love the advice available on here.
The bearings feel ok still, so I'm going to repack them and pre-load per this thread. I check the bearings for play at 12 & 6 at least every 5000 miles when I rotate my tires. I didn't feel any looseness doing that until the driver's side at closer to 6-7k miles since the last check (lost a tire to a massive cut in the sidewall so I no longer had a 5th to rotate in). I'll have to pay closer attention to that, but it's possible that it's just not loose enough to feel that way.
Any chance that having the preload a but light cause my axle seals to fail prematurely? Haha. That's a whole other mystery.
It allows the hub to move in something other than a perfect circle which then forces the birfields to turn in something other than a circle and that wobble will tear up a seal.
Also make sure you axle housing vent is clear. Remove the fitting from the housing, blow through it. I had to use a drill bit with my fingers to auger out the hardened gear oil in mine. I cleared that, then installed 5ft of 1/4" fuel hose and a fuel filter up by the brake booster to create a vent up high for water crossing.
My knuckles had taken on gear oil because of the clogged vent and as the truck cooled down after a long drive, it would suck the grease out of the knuckles back into the differential.
After I cleared the vent, that problem went away.