I have a T-5 that shifts just fine and doesn't see track duty right now. It's leaking between the bellhousing and the trans though. It leaves a puddle about the size of a cd overnight. If I take the trans out is there some kind of seal that isn't to hard to replace in there?
input shaft retainer seal (front trans seal) very simple, very easy to replace. If you're gonna pull it for that, i'd upgrade to a steel retainer, but not required if your old one is not grooved. WHen you get your trans out, it's the retainer around the input shaft. A few bolts, and it's out. Don't loose the shims, those are important. Put light silicone on it, but don't go crazy.
also, inspect your clutch. by now, your clutch is likely toast, and has trans fluid all over it.
I'd honestly take your trans to a good mustang t5 shop, and have it freshened up. If your front seal is toast, chances are that the rest are in similiar condition. I had mine rebuilt complete for $350 out the door (actually $450, but I had a busted second gear, bent input shaft, bad slider)