TH400 rebuild

[jbdetail]

I have a 67 C10 with a 427 and a TH400 transmission. I bought this spring and drove it 1000 miles home, but recently have had issues with it. It sat outside without a hood on it and the truck started to leak transmission fluid. It also did nothing when put into gear, but likely because it's low on fluid. I took it to a local transmission shop recommended by my mechanic, and they pulled the pan off and said that it looked like water had gotten into it and might need a rebuild if the clutches got wet. However, there is no way to tell unless I start to drive it. The transmission is leaking out of just about every seal it can and will need to be pulled and resealed. I was quoted $500 for just a reseal, but there still wouldn't even be a guarantee that the clutches would be ok and haven't gotten wet. The other option is to rebuild it. For a full rebuild he estimated $1000-1200 depending on what needs to be replaced, but likely just soft parts. I think I am leaning towards a rebuild and be done with it, but would I be able to get by with just a reseal? Would rebuilding it add value to the truck? I was thinking about selling it in the nest ~year as well. Are these prices reasonable? Or any other thoughts?