Having trouble diagnosing a wiper problem. I believe I have the 14W Lucas unit although it doesn't have a Lucas mark. Without the blade on the shaft rotates fine. With a wet windshield the blade rotates OK, but as soon as the screen dries even a little the arc rotation is greatly reduced, the speed is very slow, and it doesn't park right. Originally the wiper worked fine even dry. This is a new unit. I'm not fond of Lucas electrics, but replacing it with another brand could be a real problem considering the spatial confines of my SPF. I took the motor apart. No apparent shorting, etc. Any help appreciated.