I agree with Milligoon - sounds like a problem with the park position switch. This is effectively a secondary circuit that continues to send power to the motor when the stalk's been turned off, until the wipers reach their parked position, at which point (detail dependent on design of the motor) a non-conductive segment on a gear wheel will break the circuit. If it's got wet, or some in some other way the non-conductive bits have become conductive or vice versa, this system can get all out of sync, and not bring the wipers back to the right place before parking them.
Probably well worth a take-apart/dry-out/clean/reassemble cycle before buying new bits.
My Mog doesn't have an intermittent setting, unless you count the judicious and regular prodding of a left forefinger
