99 2500 burb transfer case

Hi everyone i'm new to this forum and am looking for some help.
I've got a GMC 2500 series suburban with the electronic transfer case.
the truck is set up for towing, 454, 410 gears. I tow a 31 contender, about 10,000 lbs. I've had great luck with the truck so far but recently have a oil leak from the transfer case. After replacing output seals we discovered that the back half case (housing) is porous. It has two small holes that have been pouring fluid. My mechanic tried to seal the holes with epoxy but it didn't work. I was told the case is magnesium and can't be welded. Any suggestion?

I have read another post refererring to this problem also and occasionally some casting problems occur and leaks may develope or exist basically as defects. That is what I understand, but I am not clear if any of these defects have been covered under warranty. Good luck.