Water pooling around base of furnace exhaust pipe

Hello;
I have a new Goodman GMH95 furnace, installed several months ago. Recently I noticed some water pooling around the base of the exhaust pipe.
Hope this description makes sense. The PVC piping coming from the outside fits into a PVC collar which in turn appears to be attached to a flat plate. The plate is bolted to the top of the furnace with four screws. I wiped away the water and watched more water slowly appear as if it was coming out from between the collar and the plate. The furnace wasn't running at the time.
The plate screws have rusted enough that I can tell this has been going on for a while. There isn't any evidence of the water coming from the outside of the pipe.
Any ideas as to what could be causing this ... maybe a sealant just needs to be applied? I'm guessing that if I apply the sealant myself, I'll be voiding the warranty.
Thanks in advance.
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You asked this question on January 4th, and people gave you several good responses, the best of which was that since it's brand new, it's still under warranty and the installer should fix the problem for free.
CALL THE INSTALLER.
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My apologies. I did an advanced Google search using my email address and my original post didn't show up, so I thought it never made it to the server.
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