I've removed the center differential part(s) from a 2001 subaru legacy to find that one of the internal parts lost its alignment/position (began to move axially) and began wearing away small areas of the aluminum housing. This has resulted in fine aluminum particulates in the gear oil. To clarify, the center differential is in a aluminum housing bolted to the rear of the transmission, sharing the gear oil lubricant. I have not removed or disassembled the transmission itself. Disassembly of the transmission is not likely to happen.
I'm hoping to flush out as much as I can with a couple drain/fill cycles of gear oil. However, I realize that this will never completely remove all of the particulates.
My question: Will any remaining particulates cause further problems internally in the transmission? Would they wear out bearings or other internal transmission parts? I assume the hardened steel gears can deal with the contamination. I checked a parts diagram and don't see much other than roller/ball/thrust bearings, splined shafts and gears in the transmission.
Edit, follow up question: Would using an lighter or different oil in the transmission for a short time (1 of 3 flush/fill cycle) help wash down particulate/contamination and or would that cause other problems with the residual oil that would remain in the transmission.
Parts diagrams/reference from Subaru