I have a TH350 trans that leaks if I let the truck sit for more than two or three weeks . If I start the truck and let it warm up the leak goes away . Also theres no leak when the truck is running just when sitting . I changed the filter and gasket about 10 hrs ago hoping to stop it . If it is the seal why doesn't it leak when running ? What seals the pump to the case ? The trans works fine so I don't want to rebuild it until something bad happens .