Kitchen Aid Waste disposal plug

Recently, my cousin asked if I could repair a plug for her kitchen waste disposal unit. The plug has a magnet fitted to it which activates the unit when fitted, presumably to stop you disposing of your fingers whilst shovelling the stuff to be ground up down it. The plugs are no longer manufactured and hers had sheared off where the aluminium alloy handle is fitted to the nylon body. I drilled out the handle and tapped an M5 thread into it, then fitted a stainless steel screw (M5 x 40mm) with so