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Some silicone sealants are more gluey than others. I've had great success with Gorilla sealant. You can get it in a fairly small size and it keeps very well after you've opened it. I've used it for china mending. But there are some plastics which are extraordinarily difficult to glue.
Have you got a hot melt glue gun? The standard glue sticks might not work but there is quite a range of industrial glue sticks available from specialist suppliers.
Silicone sealant.