If the IRD was new and this is its first oil change I would not worry about the fluff on the pickup as long as it is fluff and no chunky bits - this is just from the bedding in process but with a new IRD I would have replaced the oil a couple of thousand kms after installation to get rid of this wear material.
My guess would be that your other issues are gearbox/clutch related an unlikely to be IRD. When a VCU fails, while it is possible to damage the gearbox it is unlikely as the weak spot are the rear PTO bearings in the IRD and the associated rear PTO crown and pinion un meshing. The front drive differential and drive in the IRD are usually no impacted - of course if the damage is catastrophic with shrapnel every where the whole IRD is taken out.
As I said my guess (and it is a guess) would be the clutch/gearbox.
Garry
REMLR 243
2007 Range Rover Sport TDV6
1977 FC 101
1976 Jaguar XJ12C
1973 Haflinger AP700
1971 Jaguar V12 E-Type Series 3 Roadster
1957 Series 1 88"
1957 Series 1 88" Station Wagon
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