I have the typical slipping main drive gear issue on my 4-4-0. To have a look at the gear box, I removed the 8 screws holding the cover plate, but I can't remove it; it is stuck on something that I can't see, perhaps a wire. The problem seems to be on the rear portion of the plate near the chuff sensor on the rear axle. There is a little give to the plate, but it is definitely not coming out. I can only lift it a few mm. Has anyone had this issue, and can you advise me how to solve it?