95 F150 Front Tranny Seal

Took my straight 6 Cyl 1995 Ford F150 to get Tranny fluid and fliters changed.  Got a clean bill of health, said it had just a bit of metal in the pan  but basically it looked good.     After driving an hour it dump the tranny fluid.  Went back they said this happens at times they added fliuds and resealed with silicone.  Another clean bill of health.  After driving an hour it dumped fluids again.  Now the say the front seal is bad and they need to take the entire tranny out to fix it for $375 dollars.  All this after a maintence change?