The driver's side windshield wiper on my 244 Volvo sedan recently flipped out (literally) when I had my wipers on, flopping oddly before ceasing to move at all aside from very minor movements.

I found a socket wrench and tightened the nut, and thankfully it seems to be holding fine. For now. I keep this in my car in case it gives again.

What would make it do this, and what would prevent is from recurring? It is the rainiest of rainy seasons here in the 'lovely' Pacific NW now, and I'm safe to predict that the wet stuff will be falling daily until next June.

Is the nut/bolt bad possibly? Worn? Or is the arm bad? Motor?

What typically causes this?

Thanks in advance.

Cheers.