Today I had this ribbed hose that's located in front of engine and near the radiator replaced. I was told it carries tranny fluid and was leaking. Is this a common leak and is it serious?

Also, yesterday, I noticed that the rear part of the tranny pan was seeping fluid. After driving a considerable amount of distance, I saw some light smoke coming from the under carriage when I stopped the car. I got out and looked under and noticed oily stains on the exhaust and rear part of the car, near the driver side rear tire. Funny thing was that I've never noticed that before (no puddles and no oily stains under car when I check there occasionally). I had it checked today and they suspect that the pan was not tighten hard enough.

What I find weird is that shouldn't the car show signs of seepage if the pan was not tighten enough in the beginning? The noticeable ATF on the under carriage seemed very sudden. Maybe there was a tiny leak on the pan gasket that I did not detect and it suddenly opened up. Anyhow, Is this something to worry about? There are no signs or drips on the floor, and today I had the pan tightened. Everything seems fine now. As much as I hate to hear any more brutal and discouraging truths, I'd like to hear some professional opinions. Thanks.