Solved.
Replace blown fuse; and, for good measure, soaked LP orifice in 99% isopropyl alcohol for an hour.
Running the last 6 hours on LP, in the direct sun, and the temperature in the fridge part of the fridge is 1 C (34 F).
I reassessed the amount of rust/scale that came out of the flue. Actually, it was quite a pile. I don't think it would have been cleaned out if I had just used an air compressor to blow it out.
In my case, at least, sliding the fridge out to do a proper maintenance job on the flue/baffle was worth it. It's like we've got a new fridge!
Issue closed.
Thanks for all the advice,
Art
