We have 8 99-2000 Blue Bird conventional buses that started breaking seat bolts, at the isle mounting. Found the 1/4" bolts rusted through at the point that the bolt went through the floor wood. We replaced all the isle bolts and found almost 1/2 of them bad. If your district is in the rust belt an inspection may be in order.
Thanks for the tip, I'll add that to my list. I have a bucket full of new bolts/nuts from a CE white install a few years back. Drill them out an put in 5/16.
“The good thing about science is that it's true whether or not you believe in it.” Neil deGrasse Tyson