I had a similar issue when the slide failed to stop when extending outward and busted a little of the trim before my wife could release the button...don't know how far out it would have gone. But, after checking with Northwood, we decided the culprit was something called a "resettable fuse" that was not sensing the added voltage draw at the end of the slide extension and allowing the slide to continue to be pushed out.
I located this little fuse in a box beneath the bed, found another replacement, and now all works well. But each time the slide is either sent out or withdrawn I am VERY alert to watching for the "end of travel" positions and making certain it stops at the proper position.
This small "resettable fuse/breaker" can, and will, cause a fellow a lot of anxiety if it fails. It is located at different locations depending on the unit.