Some of the windscreens you can purchase are in fact thinner than the original units supplied from the factory. This can make them a little more difficult to fit but another unexpected thing i have noticed is the engine and outside noise is more apparent in the cabin. I suppose it comes back to the old adage you get what you pay for. Sikaflex should not be used as a sealer if required as it is a hardening sealant that is used for late model flush fit glass. A mastic sealant stays flexible and allows flex.