I would also take off all connections to the starter motor, give them a good beasting with a wire brush, put them all back on ( in the right place?
) and cover it all with vaseline.
When you start the car you are placing a huge load on the starting circuit and its pulling loads of current.? If you have a poor (for poor read resistive) connection there will be power lost in that connection.? As it needs this power to start it has to draw extra current to turn the engine over so takes it from anything else that might be on, like the clock in this case.? This causes an intermittant power loss to the clock and it resets itself.
Just a guess, at worst you'll have excellent connections for the coming winter months.
