Well, it's far from amazing tech but I serviced the rear diff in an '85 K20. I gotta say the semi-float 14b is a pretty good axle with an impressively long run. My parents' 2006 1500 VortecMax uses virtually the same unit, albeit 6 lug and somewhat different drum brake internals.
Anyway the gear oil was more the color of weak chocolate milk. Obvious condensation or water intrusion over the years, but nothing outlandish, either. For all I know it's the original fluid from '85. The diff cover was retained with orange RTV -- no idea if that's what the factory used.
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A decent amount on the magnet, but again, not unexpected.
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Bit of rust on inside of cover
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Cleaned up and Lube Locker to go in
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Like I said: hardcore tech