Windscreen wipers not parking properly.

[Grommit]

Hi all,

had a problem with the wipers on a recent trip. driving along quite happily using the wipers occasionally, on intermittent, suddenly they started parking in the middle of the screen . sometimes near the bottom, sometimes near the top, until they settlesd at about 45 degrees.
Tried changing the relay, same problem.
Tried loosening the nut on the motor drive shaft and turning the linkage back to the park position, whilst kepping the motor still,  same problem, which is really confusing, tried it a few times, always return to the same position.
The motor seems to want to park the wipers with the drive crank straight up, irrespective of its position on the drive shaft.
Where does it get the park position from, i would have thought it was something in the motor, but clearly not as it parks the wipers in the same position irresppective of the motor.
Anyone have any ideas waht to try next?

Thanks