Thankyou all for your input -

I've come to the conclusion that I'll just install the ribbon strip that's on it's way to me (BMW LCD display pixel failure repair KIT - E38 E39 M5 X5 - LCD display pixel repair ribbon - instrument cluster OBC) and put up with the cracks in the perspex face.
Maybe I can source a dead cluster and just strip the case off it to get the perspex.

I'll "post before and after" photos in a couple of weeks when the ribbon arrives and has been installed.
The photos on their site look impressive, but I'm wondering if just the new ribbon will do the trick, as they say, or if I'll also have to buy a new LCD.

Rob