If the Bakelite cap feels loose at this point, after a couple of light taps, you will need to de-solder the strap jumper on the small terminal, then it should wiggle off. If the cap still feels tight then it is crimped on, and not removable.
Thank you. The cap never came loose. Just the connecting bolts came loose.
I think I will spray it heavy with electric contact cleaner and see what happens I do not know of anywhere to get parts for this. So trying to not ruin anything.
a quick online search shows several sources for a replacement if you can't get this one to work. Search DKJ1308 solenoid.
After you get a new one on and working you won't have to be timid about taking this one apart.
If this is the type of relay/solenoid that has a motor to engage the Bendix drive, then never mind. But if it is just acting as a relay then you can simply use a regular starter relay switch that has no solenoid.