One of my 240s heater boxes is leaking AC condensate out the center seam. Water is running down into the driver side floor pan. I first suspected a clogged drain hole or hose, but both were fine. It looks like I'm going to have to pull the heater box, open it up and re-seal the seam. What is the best sealant to use between the two heater box halves? I don't want to have to pull it all back apart again a couple of years from now.

I will probably replace the fan motor while I'm in there too. It's starting to make a little noise. Should I also replace the heater core too? It is a 1990 with only 110K. I know some of the original parts can be far superior to any aftermarket ones. Is this the case with the heater core? How long do they typically last?

The HVAC system is one of the few gripes I have with this otherwise super fine automobile. Its like they built the whole car around the heater box. I also noticed that if the car is sitting level, the condensate drain is not the lowest point in the box, so some amount of water will always stand in there. I guess I could park backward on a hill and partially alleviate the issue.

Thanks,
Preston