I have to use a heater in my darkroom too. Worst problem I've had with them is the thermostat would seize up and run wide open. I'd check on the darkroom and find it running about 80F instead of the 68F it should have been. The mini ceramics gave up the quickest. I have a large electric from Home Depot now that seems to be holding up well.
I have to run the heat so low I'm tempted to find a high power dimmer to run it on so it will have a longer duty cycle so the fan will circulate the warm air and dissipate cold pools.
One thing I found about the oil filled type is the thermostat mainly regulates the oil temp and if the environmental temperature varies much you will have to turn the thermostat up or down to keep a constant level of heat.
The damaged ceramic heater got integrated into a film drying cabinet with a dimmer to control it, using only the low power leg of the core.