I have a Defiant 2in1 built in about 2010 that has chronic problems with the refractory cover. After replacing several that cracked, the new one began falling out of place after two years of use. At $90 a piece I'm reluctant to buy a new one until I know why. Maybe the cover is worn down in size so it's no longer a tight fit or is there another problem with its frame? Anyone have a similar issue?