Same here: the instructor who checked me out in N2966V told me to disregard the checklists and not to switch the fuel off, ever. Breaking it off is a real possibility. The fuel switch was one thing that I really hated about flying M20E. The "off" position there is between "left" and "right", so you have to pass it every time you switch tanks. The switch is also ridiculously stiff and also small. I was sweating bullets at every tank switch. Insanity, truly. One of renters created a special tool: a crank fashioned out of a PVC pipe that permitted to switch tanks somewhat more easily.