I've been informed by a tech that the "coating" is gone on my '86 Bryant secondary HX. An unusual sound (intermittent louder humming/vibration) brought the problem to my attention which the tech thought had to do with the moisture accummulation. It's out of recall range and obviously due for replacement. I'm looking for a new furnace, which I also have questions about for another thread, but need to know if it's safe to run the furnace in the meantime. The tech said it would probably shut down before CO is a problem and only one of four estimates so far have voiced any real concern about it. Please advise.