[Humber888]

Loctite 'All Plastics' superglue is specifically designed to bond 'soapy' plastics such as polypropylene, polystyrene, polyethylene, PTFE, etc. It's a two part glue with an 'activator' and also glues china, rubber, metal and wood. I have used it to successfully repair all sorts of cracked plastic, including the gears on an HP8640B. Don't use it if you just want to surround a weak point with something that will harden off and provide some additional support. Expect to pay at least £5 for a small tube and buy it only when needed as it does not have a particularly long shelf life and tends to bung up the nozzle.