1999 Buick Lesabre Not producing enough heat, big water pud

Had intake manifold gasket replaced June 09 (at the dealer). Since then, I have had a huge puddle of water on my garage floor (5' long x 3' wide) it never goes away. Cold to luke warm air when climate control is set in the 70's. Have to punch it up to mid 80's to get heat. When I do that it sounds like a little door slams open and heat just pours in. It was suggested that it might have a clogged heater box hose. Any other ideas? Am I in for big $$$ repair bill? Thanks

updated 1-26-10

I had the car in at the dealership on Tuesday of this week. He checked everything. All fluid levels were okay. He pressure checked the A/C unit. Could not find anything. So the plan is that I clean up the garage floor (which I have done) and wait and see if a puddle forms. I haven't had the car out on a run since cleaning up the floor. As far as the blender doors go, I had done some research before going to the dealer and found out that it involved removing the dash etc. - Very labor intensive. So I said forget that problem. If the heat finally totally stops, then I will try and see if they still make those little heaters that can be plugged into the cigarette lighter. I just don't want to put a whole lot of money in this eleven year old car.
Thanks for you reply.