Securing upvc cover for end of windowsills

[Longshanks]

Hi

We have a few sills where the cover for the end has worked loose. (Glue dried up)

Just wondered what species of adhesive I’d need to buy to re-attach?

Many thanks

 

[crank39]

Looks like they used silicone but it doesn't like to stick to smooth surfaces so I used to get the point of a new Stanley knife blade and score some cross hatches in the back of the end cap, helps the silicone to grip something

 

[Longshanks]

Cheers

 

[Harry Bloomfield]

The denser, clear sealant, seems to stick much better.

 

[Longshanks]

Thanks. I know I have some of that.