I'm no car expert and I've never owned an Allison tranny. However, if it was me I would keep watching the fluid level, I would keep some extra fluid handy to top off, and I would buy a shallow pan to catch the dripping when I parked, if there was a lot of it. And I would keep driving.
+1 on the full tranny rebuild, but I see this as at least 20,000 miles out, maybe much much more. When I buy a car it's because I love it, and I hang on to them for a lot more miles than the OP has. The idea of selling a car after you've just covered expensive repairs is silly, IMO. The new tranny will take this rig to its Final Rest, many many miles from now.
