Not sure on the rebuild. If you crawl under it you may see the leak. If it's a leak from teh transmission pan, you can probably get a new pan for maybe $400 or so. If it's a seal or something internal then you're looking at a rebuild, but I can't see a rebuild costing any more than $2000. So you're talking $4000 to get it right. Mine is a bolt action, so I really don't have much perspective in that sense.
I'd check the radiator to see if it's full of junk; if so you'll need good flush or maybe new radiator. Also, take a note of the timing gear cover. It's on the front of the engine on the driver's side. Look around the edge towards the center of the engine for a bolt or something screwed into it. If you don't see it, ask the owner if he knows if the dowel pins have been tabbed or fixed. That's about the only engine issue on these trucks for the most part. Ask for the maintainence records if they're available. How many miles does it have? I bought my '93 (see signature at bottom) for $6000 and except for needing a paint job it was in mint condition with 150k miles.
had a ford 6.9 with banks kit and it was 
not even in the same ball park as the mighty cummins
