Ok everyone. I changed the o-ring on the sensor but somehow the bolt fell into the wormhole that goes to the "Missing Crap from my Garage" dimension. It now has many nuts, bolts and tools of mine!
Anyway, where can I get a new bolt?

 

Basically any decent hardware store, it's a M6 - 1.0 x 20mm

 

Thanks! Got a bolt and it is back together! Oh, and I bought an extra!