Have had good luck with JB Weld for such. You know the drill ... solvent clean surface , rough it up some. On a nice dry day layer on that plastic metal crap in a tube till thick. Have saved two saws w failed oil reservoirs , JB held long enough to finish life of Powerhead.
You could get creative and use a piece of nylon on the bottom ,bolted with counter sunk flat head screws through the handle extended forward of the tank so you don't drill a hole in it .I've done similar repairs using aluminum plate . You can machine nylon just like you can metal,drill and tap,anything you want except arc weld it .