[1969 GMC]

I have slowly been taking apart the D60 I got at the junkyard, and the tubes are FULL of crap. Nasty, dried gritty dust/dirt type stuff.

I think a seal would be cool. It will be easy for me to clean out the tubes since I am disassembling the axle entirely (pressure washer) but for guys just doing rebuilds I've heard it can be a PITA to clean them out. There is/was a thread on Pirate about someone making tube seals, I think it would be a neat idea. If you're still worried about contamination, just pump the tubes full of grease, and perhaps put a drain plug in the tube.