brake reservoir inspection window popped off

[chinaman]

Received my new 150 cc sunny scooter friday, assembled it today and it started right up everything is working fine. Problem is, on the right hand handle bar where the brake reservoir is, the little plastic see through cap popped off when i started it, it's leaking brake fluid. Does anyone know if I can glue that in? Looks like it has a rubber gasket on the inside and threads but I see no way of screwing it in...looks like it may have just been stamped on there some how. Anyone know?