I don't think it can be welded. If you're not interested in getting a new one you can try this. It might just do the trick. You can look for it at Montgomery road. There is also a shop at Waris road that deals in liquimoly products
RADIATOR STOP LEAK
Stops minor leaks, and seals cracks permanently and reliably. Protects combustion chambers against damage due to entry of water. May be used with all types of radiator anti-freezesandcooling-systemconditioners. Suitable for aluminum and plastic radiators.
Operational area: For all water-cooled engines, to stop water leaks and seepage, and to prevent future leaks. One can is sufficient for up to 10 l of radiator liquid. Application instructions appear on the container.