Its a fairly unorthodox question this one, as presumably the missing ventilation flap was actually hinged....however, no matter. If you want to seal the hole, find a plastics supplier in Yellow Pages and ask them if they can supply you with a piece of 6mm thick polycarbonate sheet (trade name is Lexan) ready cut to your size requirements. Have a look at the problem - can you fix the piece of plastic in place with self tapping screws? If you can, have some silicone sealant at the ready...the stuff that seals bathroom fittings and smells of vinegar. Genuine perspex (acrylic) is brittle and is easily split or cracked when drilling...polycarbonate sheet doesn't. Hope this helps!
John, July 2009
