John wrote:

Can anyone suggest a suitable glue, metal putty or whatever which would
stick into the slot in the metal and stay even with the pressure of the
water?

Those two part leak sealing epoxy putties would do the trick - DIY sheds
sell it in short strips of two colours where you tear off a bit and mix
it until uniform in colour. Sticks like the proverbial to a blanket and
sets hard.

--
Cheers,

John.

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