I'm not sure what the original resistance of the device was but about 1-2 k is what works empirically feeding the next stage which I haven't attempted to measure the input resistance of.
This device is about 9mm in diameter - I'd guess simply a tube with the bulb at one end and the whatever at the other. It has a symbol for a bulb and a resistor to denote the ends, so I assumed it was an LDR. It's quite big enough to allow fabricating a replacement mechanically easy.
I'll do just that.