Advice on NP203

I pulled the NP203 outta my '79 GMC K-1500 today (actually, it kinda fell off the bracket I had made for my jack, and i luckily pulled my arm out of
the way before it managed to smash it), and as the oil started to pour out, it was pretty rusty colored. I pulled the front output shaft rear bearing support plate off, and the bearings are still in good shape, but there's quite a bit of play in the chain (I guess after over 20 years, it's got that right). Should I replace the chain and flush the insides out? Should I completely rebuild the damn thing? How should I flush the case if not rebuilding it?
Any advice would be greatly appreciated....
-- It has become appallingly obvious that our technology has exceeded our humanity. -Albert Einstein
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