I've read some interesting
thread on ht.com about repairing a faulty 4WS unit. I don't know if it was posted also here on PO.com.
I opened the unit as described in the thread and saw 2 big and well visible cracks:
I resoldered also the other points just to be sure, because the cracks are usually not visible, this is an extrem

.
I havent tried the repaired unit yet, so I can't say if it helps or not. These cracks are not good anyway.