there will probably be a link rod from the outer handle to the inner lock assy,whether the fault is with the handle or lock will only be known when the lock assy is stripped out.The white plastic cover you are on about is probably an anti-theft device and may be held on with pop rivets/screws which will have to be removed first for access.Disconnect all cables/wiring and I think the key barrell has to come out also which will probably be held in with a large horseshoe clip and the key also have to be inserted and turned a/clockwise to release plunger to turn out barrell,then hopefully you can see what is causing your problem,a while since I done one of these so hope all the info is correct,good luck
cdc, August 2012