Exhaust fumes (?) through the defroster and heater vents?
(1) Probably. I refuse to use ANY of these additives. I don’t trust any of 'em. But that’s just me.
(2) Honestly? I don’t think any tech worth his experience will touch it. You can tell him what you know about the stuff, but stand back when he throws it in the trash can. (Kidding)(maybe not)
No offense implied, but I’m not into Jeep (or any other Chrysler/Dodge) and suggest that if you want to keep this vehicle, either have the heads AND the block planed and reinstalled or replace it with a rebuilt motor.
Perhaps the head gasket(s) were slightly damaged during installation.