I have a Bryant Model 398A, Deluxe gas-fired condensing furnace, vintage 1987. The unit performs well but recently I noticed a raw propane smell outside my home which is coming from the furnace exterior discharge vent (3 in. PVC pipe). A repairman found and corrected a couple of minor gas leaks within the furnace, but the raw gas discharge, confirmed with a "sniffer", continues. Any ideas on where to look for this source would be appreciated.

The furnace itself should have complete combustion of all the gas that is fed into it. I hope the furnace man checked for that since there is no other way for raw propane can come out of the furnace discharge line.. Have you considered the leak is outside to start with and not from the furnace?