Please tell us more about the tube that was leaking. What was it? There are
only 2 tubes coming out of this transmission, to my knowledge, and they are
to and from the oil cooler in the radiator. If you rubbed a hole in one of
those (I can't see how), or hit something that holed or caught on one of
those tubes, I suppose you could lose fluid. Have you serviced the
transmission before in it's 165K life? Fluid and filter change should be
done about every 30K or thereabouts - if it hadn't been done before, I'd say
your transmission is in need of a rebuild. The guys that changed your fluid
should have been able to tell you what the bottom of the pan looked like and
how much wear material they found there. Also, the color and smell of the
fluid would have told them if the transmission was due for an overhaul.
Where did you take it - a real transmission shop or a oil change place?

As far as the Check Engine light goes, you could easily have that read by
someone at Auto Zone for free, and they'll tell you what it means.
Normally, error codes stored in the CEL system will not prevent things like
transmissions from working.

I'd suppose that for a rebuilt transmission, you're looking at about 1500 or
so. Probably more, knowing the labor rates of the shops around here. Not
sure where you're at.
Steve