hi, recently the drivers side and rhs rear window have become stiff in operation ,sometimes jamming mid point and with a crunching noise when lowered or raised, the rear one has failed to lower now but it is in the raised position thankfully. it this a problom with the door regulators does anyone know? what parts would i need to order to rectify? i intend to repair myself but dont really want to dimantle the door twice if possible. thanks in advance, brian.