Over-tightening the focuser would not normally achieve that result. I would investigate the true cause - if the product came with an overly long screw that struck the mirror when you racked it all the way in for the first time then Meade are quite probably still liable to fix that issue under Australian Consumer Law, which does not expire after 12 months as some believe.
Otherwise, a splash of matt black will do the trick, but even then I would only do it if you can see light scattering on bright objects. Just be careful transporting your OTA with that shard of glass rolling about inside
