Long story short, I broke my upper last year, so I had it rebuilt & I asked my drive guy if he should inspect the lower & he said it should be fine... well that lower lasted a couple hours & exploded, so my question is should I have the recently rebuilt upper disassembled & inspected? I ran a couple quarts of clean gear lube through it hoping to flush out any metal.. I have a rebuilt lower to put on .. not if I should spend $$ having the upper checked out again? I pulled the back cap & the gears look clean & just a trace of shavings on the upper magnet

First, find another drive guy. That is a lazy approach.

Every time I have a failure my drive guy pulls apart the lower unit. I never want to pay for it but, as you can see, its worth it.

The upper has critical bearings and one small piece of particulate in the wrong place and you are out another $3500. You might get away with a flush and an oil change after the first hour but see what others have to say... My 2 cents, not worth it.

www.allamericandriveservice.com

That is correct, anytime there are metal fragments the whole drive should be disassembled and cleaned and checked for any damage. The lower gears act like an oil pump and send the oil and metal fragments up to the pinion bearings on the input shaft. That cavity will hold and hide metal fragments. The pinion bearings may be damaged causing the preload to loosen, then the pinion gear moves back and forth and eventually something breaks. The oil also circulates to the lower from the upper and brings metal particles along with it causing similar damage to bearings in the lower.
Just makes sense to have the upper/lower looked at when there is a failure.

Hope that helps.
Dick