Finally got the manual transmission fluid changed, and I did it right - pulled the top of the tranny to overfill it. So, it helped to get the carpet up some and I found that there was some dampness on the passenger side near the dash. I have heard of AC drains causing problems, but don't know much more than that. Any advice?

Yeah, could be your AC drain, or maybe your heater core has developed a crack.

any tips for finding the source of the water (drains, etc.)?

If it smells like anti-freeze, it is a leaking heater core.
The A/C drain is a rubber hose under the passenger side firewall IIRC.

What probably happened is that your AC drain is clogged and the water is spilling out of the joint in the evaporator case where the two halves--top and bottom--come together. You will need to take the bottom half off and clean out the blockage, which is usually caused by small leaves that make thier way through the fresh air vent.

Scott

ditto on D21. It's most likely coming from your a/c evaporator.

This summer I had to clean mine out. Here's my How-to

http://nissan4wheelers.com/eve/forums/a/tpc/f/3766078435/m/77010062141 .