Hi! I have UPVC double glazed casement windows with wood effect finish outside and white finish inside installed in my house. The internal seal between the window trim and plaster seems to crack up very often. Since installation 2 years ago, I had them resealed twice. The cracks are quite bad at the bottom corner and I can feel cold air coming through. I am getting the company back to rectify the problem again this Friday. I am not happy to just reseal and wait for it to occur again. What would you suggest that I should get them to check?