weld-on,
at IPP or other plastic supply houses.
methylene chloride is the water-thin base for all of these, as far as I know.
we used to make our own thick glue by adding plexi shavings to a coke bottle of MC. ( yes, that long ago!)
Aircraft spruce has the thin Weldon #4, and Wal-Mart has the honey-like #16 tubes I believe.
sign supply places have all the stuff, including tiny plastic bottles that won't dissolve, with needle dispenser tips,
...........so you can just touch it to the crack, it will wick in, then a little pressure to 'weld' together.