"spot light bulb"? I assume you mean the light that that is on the side of body on the outside. My RT 190 is under cover for the winter otherwise I would look at my light.
Can the whole light receptacle be taken out, then you can work on it inside.
First, pull the fuse. I would try some liquid penetrant first, PB Blaster or Kroil (difficult to find) are far more effective than WD 40, which is technically a water displacement liquid good for keeping things from rusting. Soak it over several days and gently wiggle it both ways to loosen it up. If there is major corrosion between the bulb base and the receptacle, you may have to replace the whole fixture anyway.
Show us a picture so we can see what the broken part looks like.