I have a Weather King 90plus upflow Gas Furnace 75,000 btu,approx 15 yrs old.Recently I have discovered water leaking into the bottom of the plenium by the blower motor. I replaced all the plastic hoses for the evaporater system and I'm still getting water dripping? I had a Furnace Man look at it and he thought it was leaking from secondary heat exchanger? Would this be the cause?maby a blocked drain tube?