That is the correct mechanism. It looks like it is missing a screw.
Here is a link to the part manual
http://www.planetarypinball.com/mm5/merchant.mvc?Screen=BOOK
And the page you might be interested in
http://www.planetarypinball.com/reference/partsmanuals/WMS_Parts_1977-1978/index.html#/38/
I would check to ensure that the switch is clean and is making contact when the ball in the kick-out hole. (the lower leaf of the switch should move a little when contact is made.