When they removed the cap, they said it was not there? That does not make any sense at all. I think they are lying.
My guess is that they did not put in the cotter pin to keep it from loosening up. Over time, it came loose and the nut and washer came off inside the cap. They just did not tell you that.
That is my opinion and will be very hard to prove since so much time has passed.
Tuesday, March 10th, 2020 AT 2:30 PM