I just figured at the track the better washers would be more suited.
That zip tie fix looks like it'll do the trick.
If the plastic lets go maybe consider a pair of wires straps wrapped around much smaller screws. (1/8" or about 1mm)
Ya take some copper wire, say 18 gauge and wrap it around a pair of screws, fasten screws, then wrap wire segments to pull the 2 bumper sections together.
^^ an ugly sketch.