i read for years that the factory block heater will crack the block around the area of the heater thats why I never bothered to fix mine
I think it was only the early 83-84 ones.
https://www.oilburners.net/threads/pics-of-early-6-9-crack-around-block-heater.60578/
The old cord on the 85 RV had been hack job repaired so obviously someone was using it at some point. The 87 truck's cord was just rotten to death, so who knows if it ever was. It certainly hadn't been in the past 5-10 years.