So I had a sudden and pretty good leak. I didn't drive further than the driveway and parked the car. jacked it up and could not directly see the leak. It only leaks after it warms up. The leak was over the tranny. So I am thinking thermostat housing, right. I am in the middle of it now. The old one looks good. How do I comfirm it is faulty? I mean like if i look at the old one should i see a for sure crack maybe? God it looks new. took me an hour to pull it out i am going slow so i put it back the same. my hoses look good. the car only has 45k on it

thank you guys