Mine was leaking into the cabin from the condensate draining out and running back up the tube to the firewall and soaking the old gasket. I had solved this problem on Dakota's for a long time, so I knew a fix for it. I grabbed about 8" of
Clear tubing, 5/8" I think, and used it to extend the drain further out and with a down slope so it couldn't run back onto the donut gasket. I had to dip the tubing in boiling water to soften the end so it would fit onto the drain, but once cooled it shrank and formed a seal so tight that no hose clamp is needed. The same might solve your issues as well with no firewall work needed.
Tossed onto the interwebs via iPhone
99 WJ Laredo - Mine once again!