My son's recently acquired '93 850 has some sort of on-off drain thing installed and I'd like to return it to the normal plug. However, I'm afraid this thing is there because sometime in the past the threads were stripped. I don't think I'll know this for sure until I remove the current valve thing.

Anyone know the cost of a replacement oil pan? Problems I'll encounter replacing the current one? Other tips?

If you do not want to do that, how about installing one of those drain plugs that accept a drain hose as is currently being advertised on network TV?

This type of drain assembly has been used on over the road trucks for some time. The have been advertised in Commercial Car Journal for at least 10 years now.

There is actually two things that keep the oil in;
A valve that is pushed open when you attach the hose, and
A cover cap that is installed after the hose is removed
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2 8s & 2 7s 600,000 miles total

Take the valve out and drop the pan off the car. Then re-tap the hole. You may have to go up slightly in size and replace the plug. Total cost including, tap, plug and new gasket should be under 30 dollars.