I dont know if the R53 is the same as the R56 because thats what I have and the rear spoiler on that is secured with screws from the rear of the hatch accessible after prying out the sealing plugs, and double sided exterior grade adhesive strip.
I would think yours is similar, but if the fixing wont tighten up because theyre stripped or whatever you could take it off and apply more double side sticky tape I suppose and refit the screws using no nails glue, of course it would never come off easy again!
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