Just recently did an inspection and the furnace blower had an unknown material and I’m not sure if other than improper seal what to say here. Any information would be helpful.
Thanks,
Mike
Heck, Mike, I have not see that before. I don’t know for sure but your “seal” guess is as good as any to refer it out because it looks like it is not proper and is coming apart. 
Might be zinc deposits. I would investigate the furnace venting for proper installation/termination.
IMO - That is corrosion from flue gas condensation inside the pipe
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Randy Mayo, P.E.rmayoInterNACHI®️ CPI
IMO - That is corrosion from flue gas condensation inside the pipe
I was thinging the same thing.
I’ve seen corrosion from flue gas at joints before but it was way more drippy.
Maybe, I’m learning something here though, Randy. Thanks.
Yep, I agree with Randy. The zinc in the galvanized coating on the metal is reacting with the condensation in the flue pipe.
This is what I am more used to seeing: 
Flue Condensation Problems
"This problem can be solved by making sure the gases are hot enough to be vented into the atmosphere. Vented up the flue before the moisture condenses in the gases. It could be a problem that requires a slight adjustment at the burner. Furthermore, it is a good idea when you observe a furnace flue condensation problem where the condensation is dripping back down the pipe, to call a professional.
They can analyze the combustion process and make the precise adjustments necessary to prevent this problem. Condensation dripping back down the flue causes the flue to corrode and rust prematurely. Flue condensation problems, if left alone, can cause the flue duct to rot and vent hot gases in an area where it could be hazardous to the occupants of the building. Furthermore, there is carbon monoxide present in these gases, and carbon monoxide is very dangerous."
From: https://highperformancehvac.com/flue-condensation-problems/