my 1983 300SD's windows stay shut. I rebuilt the console switches & magically both back windows began working! I took the driver's front door panel off to investigate.. and hooked a power source up to the motor's wires. I tried pos/neg both ways.. and each time the motor clicked, but did not budge. Does this mean the motor is shot? or is it just stuck? Is there a step by step DIY replacement guide anywhere?