My BMW install tool has a lip roughly 1.5mm (where the 0.170" is in the drawing). It also has a pilot to guide the seal lip over the input shaft.
Between the slave and the input seal should be dry. Not only do I omit the gasket completely, but I drill a drain hole. I actually have a bad slave bike on a lift now; the brake fluid ran down the pushrod and soaked the friction disk. With a drain hole he'd have noticed it before it got to the point that I had to disassemble the transmission to fix it right.