75K mile warranty locally is nice for sure. I'm just not too keen on out of town builds in the event something does happen... you have to waste another half day pulling it or shelling out. Not cool. So you're paying ~$600 more for a pretty stout warranty, that's good piece of mind.
Lubeguard has the only stuff I'd consider to pour into the unit. They have a pretty damned good flush I'd try prior to shelling out the cash. Go per the directions and see what happens.
www.transmissionpartsusa.com or
www.bulkpart.com should carry the stuff.
I too would check the dealer on a reman unit, it may suprise you.