I have a weird problem with my Yashica-Mat EM TLR. When focused to infinity or near infinity the shutter sticks open randomly. It happens at all speeds and apertures. When it sticks open it will close if i turn the focus knob to closer focus. It will also close if i turn the film advance lever.
Does anyone know what might be causing this?
I will attempt to fix it if its something fairly simple but if it will take a major repair i will probably put it on the shelf.

Thanks
RSN