Originally Posted by bevman
I have drilled out a couple of them, and then put in a self-tapping machine screw. Be certain to use a lock washer and, as I did, some blue thread lock liquid. Should be fine. Yes, they need to be cleaned periodically. Any residual oil makes for flypaper/dirt trouble that will gum up eventually. I clean them and lube w a dry silicone spray. Still, periodic cleaning is a good idea. Don't force them and they will serve you well.
The old original vent cover operators, were designed to have some internal friction. The purpose of the friction was for the operator to stay in a selected open position while the coach is on the highways. The problem with them, as they aged, was the friction part, no longer existed.
When the internal friction of those operators was history, then simple vibration would further open the vent, which in turn, would blow off the trailer, when a on coming large vehicle would pass the trailer.
That was a very common occurence when I worked for Caravanner insurance company. I am sure that the same thing continues to happen today.
A redesigned vent operator is available, that replaces the original, does not depend on any friction, since it uses a threaded rod for opening and closing the vent. Therefore vibration has no effect on it.
Lubing the original operator makes it easier for it to further open, simply going down the road.
If the friction of the old operator is gone, then make sure the vent cover is completely closed when traveling. That will stop the cover from being blown off.