The mechanics to get the tape to eject are usually not too bad to figure out once the radio is opened up. It gets a bit tougher if the magnetic tape is wound around places it's not supposed to be, but if you're lucky, the issue will just be a bad rubber belt and either a new one can be fitted, or the spindle rotated to eject the cassette tape. It's been awhile since I've had one of these open so I don't remember if the cassette eject is belt driven or direct drive. With the cover off would be a good time to inspect the volume control for conductive material transfer. I've had to repair a couple of those that would go full volume as soon as the key was turned on due to the conductive paint for the button having stuck to the contact instead of the button dome.
-Rod