well, the world may never know.
I removed the cord and checked the heater for resistance- and it had some, so I checked the cord for continuity- it was bad. I cut 6" off the end and put in a new plug- all's well, for now. I think I'll recommend a new cord from the dealer.
it has the screw down brass cap on the block end,
not like the pics from this site., so I reckon its an OE unit?