I'm a two-bolt mast base man. No single bolt uni's for me (except on the SUP which only has an insert.) The attraction is the extra safety...if a bolt fails I can still sail home on the other, though the mast foot may get out of position. Also the two bolt plates can be left on every board, and just the uni(s) can be attached and removed as needed, speeding up derigging.
End of sermon. Here's what happened at the last session: I was adjusting the mast foot position on my 99 Skate in the parking lot of South Jamesport, when, while tightening the bolts, one sheared off while I was not applying that much torque. I wasn't close to using a strong twist. That bolt was ready to fail...happily it did so on dry land.*
I'm guessing I bought the foot ten or twelve years ago...maybe more. I'm not sure how I'm going to be inspecting the others, but taking them off of the boards (I have a two bolt plate on all four boards) for a look I will be doing. Gear breaks.
*More happily I had an extra one in the van.
(Photo: The bolt in two pieces.)