There is a video on Vimeo which covers this issue in great detail. I followed each step exactly and it has solved the issue. At first it didn't work until a fellow 18SZ owner told me that you cannot have a switch specified for gear or doors in the function menu. They can only be assigned in the Pmixes. Once I removed those from the function screen, the steps in the video worked like a charm. Door even closes back up when the gear is down, P-51 style.