Just wanted to weigh in on the 'fabric covered ducts' referenced in Pat's initial post. Most heater ducting in old vehicles is what is referred to as 'cloth-inserted neoprene' ducting, but over the years, the rubber gets old and brittle from both heat and age, and leaves what looks like a fabric hose. I don't know who made the ducting for Packard back in the day, but one of the long-standing manufacturers in the US is Flexaust Inc.
flexaust.com/group/industrial-hose/ The product is CWS for single coated neoprene and CWY for double-dipped product. (recommended) The problem with a lot of the auto-applications was that the 'hose barb' fitting was a different size on the defrost 'spray diverter' and the heater itself, requiring an enlarged cuff on one end, making it an OEM replacement part. The size difference isn't usually that much, maybe a 1/4" to a 1/2' at most. Buying the smaller ID size required and then carefully snipping the helix wire on the outside of the ducting an inch or so from the end and then working the wire out from between the plies of the hose, will leave a soft cuff that can usually be stretched to go over the larger end. Flexaust may only sell full lengths (usually 25') and may not even deal with retail, but any of their stocking dealers will sell by the foot. And, if the helix wire removal trick doesn't buy you enough enlargement, I have seen the product manufactured with enlarged cuffs. Regardless, the fabric inserted product is what the vehicles started with, no matter what they look like now and replacing them with new hose is an excellent idea as when they get worn to look like cloth, they are very porous and are prone to a lot of leakage, diminishing the actual delivered air to the windscreen.
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