Debonding super glue ?

[Turbo]

You can sand back upvc and finish it with cutting compound. Just treat it like paint.

 

[Ubique]

The pr!cks that glue themselves to roads apparently have their adhered bits soaked in Coke (the drink, not the substance), maybe try that? Time might be of the essence though, what works on recently bonded may not have as much effect upon somethig that's has years to cure.

 

[Onoff]

I fitted this second hand uPVC door. Zoom in and you'll see the glue residue up the sides from where I took the trims off. I used sharp wood chisels to take off the remnants. It came up really well. I used Unger RubOut to finish off and as a cutting compound using wet and dry on stubborn spots.

https://flic.kr/p/Y6VqzE

 

[Smallfry]

I fitted this second hand uPVC door. Zoom in and you'll see the glue residue up the sides from where I took the trims off. I used sharp wood chisels to take off the remnants. It came up really well. I used Unger RubOut to finish off and as a cutting compound using wet and dry on stubborn spots.

https://flic.kr/p/Y6VqzE

That is exactly the same thing as I have, except its on the inside.

MiL has a steam cleaner thing for worktops and the like, she is going to bring it over when she comes on Christmas day, hopefully that might work, but I am not holding my breath. I may end up doing as you have.

Did you get your drainage sorted BTW ?