The weird thing is that it almost seems like the engine is starting more quickly than before and that somehow this is 'catching out' the starter motor shut-off. I really don't think that it is remaining engaged with the flywheel as that is not the noise I am hearing. Its almost like the motor is on overrun, continuing to turn after the gear is disengaged.

This also started happening in the warmer southern climes before I got back to the cold weather.

My only thought about the easier starting is that I just switched to full synthetic oil (Mobil-1 15W-50) and maybe this is having some effect.

How easy is it to pull the Starter Motor for a check-out?
Can you purchase new brushes and if necessary a new solenoid, or do you have to replace the entire Starter Motor?