I bought my z4 last september knowing that it had a problem with the roof,po had pulled the lever in the boot to allow him to open the roof manually,anyway fast forward to yesterday,i finally thought id have a look see what kind of shape the motor was in,when i got the motor out it was a little bit damp but seemed to be in ok nick,the bypass valve was jammed in so i freed it off and connected the motor to a battery and hey presto! Working motor!ive activated the cable over and over again to make sure the valve was opening ok and then refit the roof! One happy( easter) bunny 
