Sticky starter motor solenoid

[Mike-]

...is my guess.

Every now and again when I go to start the car the starter is refusing to disengage. The key returns in the ignition and when I turn it back to the off position the starter is still whirring away making a mess of my flywheel.

Given the ignition barrel seems fine is this likely to be a problem with the starter itself or maybe just the solenoid? Is a dab of carb cleaner safe to use on the connections to clean them up?

Thanks,
Mike.