Help me diagnose my D6c final drive

About two years ago I had the LH final drive worked on. Bored out and put a bushing in to get the dead axle back to spec when it's pressed in. At the same time I put on new chains, sprockets and rollers. Not long after I noticed a clunk in the undercarriage I hadn't noticed before on the left side. I kind of chalked it up to new undercarriage being different. Didn't use the dozer much the next year, but used it quite a bit last summer cleaning out a pond and pushing out fence and a lot of trees. I began to notice a clunk again in the LF final drive, and found that it only happens when backing up a slope and shifting to forward. It's a pretty good clunk but if I idle it down more and come to a complete stop before shifting to forward, it doesn't do it. Doesn't seem to do it at all shifting from forward to reverse. I dropped the oil (80-90W GL5) out of the final and found some steel fuzz and some small flakes but no big pieces. The odd thing is the oil also had quite a few brass flakes and the oil had a very pronounce brass color. As far as I know there are no brass components in the final drive so I don't know where it could possibly be coming from. I don't think its a seal problem between the bevel gear case and the final because I don't lose trans oil and the final drives don't get over full. (the finals don't leak either) I also dropped the oil out of the other final drive and it just had a small amount of steel fuzz on the magnetic drain plug. There might have been a tiny amount of brass color in the oil but not enough to notice if you weren't looking for it. One guy I spoke to said he had seen some final drive pinon bearings that had brass bearing cages but that's the only possibility we could come up with. I also backed off the brake band on the LH side, pulled out the access plug on the side of the bevel gear case, and used a pry bar against the clutch drum to see if I could detect any movement from a loose bearing, but couldn't see any. I suppose it's possible the bearings on the second reduction gear could be loose but there's no way to see it. Anyone seen this before? Do I put in new oil and watch it to see if it gets more brass/steel accumulation?....or is it about to grenade on me? Here's most of the steel I could fish out of the oil with a magnet and off the drain plug. Funny thing is it looks like some of the brass is picking up on the magnet, but I suppose it could have some steel imbedded in it from going through gears. The next three pics show brass flakes and brass colored oil