That sounds familiar - from what I read at the time the control module contains a pair of MOSFETs which are designed to drive the motors - the theory was that when the motor seizes (or maybe the pads are not adapted properly) the motor pulls more current then the MOSFET can supply and so they get slowly cooked.
You can watch the current supplied through measuring blocks - I still have the old module on the shelf which I intended to open up but never got round to.
Again this is a distant memory, but think the cost of the new module was in the order of a couple of hundred pounds, so not cheap but was money well spent in my case
