Scary pre-flight finding

I have had the RV tied down outside on a grass field for a few days (drag racing at my home airfield). While removing the tie-downs I saw a problem.

I always check all flight control surface connections during each daily pre-flight but I now realize that I almost always only check this flap hinge attachment from the bolt head side, I usually never look at it from the nut side. This incident shows that I have to change my walk around routine.

Picture showing the problem:

Washers, nut and lock-pin is missing, how many flight have I done with the missing hardware?

 And how it looks after a 5-minute fix: