It occurred to me, (on the way back to the shed after reading the helpful remarks about fan removal) the fan is probably held in with hot glue. The weather is cold, the glue is hard and unyielding. OK. Apply hot air from heat gun to fan unit, when thoroughly warmed through, apply pressure. The photo proves that it worked. Kadet in background with front blue trim finished, awaiting some idle bloke to apply finishing touches (black pin stripes)