Dr Paul Leyland

There is stuff here in La Palma called “No mas clavos” made by an outfit named Pattex. Literally translated this is “No more nails”  and a quick web search suggests that it is the same as the UK product.

Regardless, it sticks almost everything to almost everything, is flexible and waterproof. I used it to get an extra 3 months wear out of a pair of sandals when their soles became unbonded, so I can testify to its strength and flexibility.

A 250g tube cost only a few Euros a couple of years back.

Might be worth investigating.

Added in edit: See