how to remove vehicle speed sensor?? 91 L FWD

my mom took her car to outr local mechanic dopwn the street, he doesnt deal with imports but hes our friend so he does for us, now all of the sudden her speed/odo quit working a and the CEL came on, im assuming he read the codes and it was the VSS, or whateeve functrions as that on a subaru, this is a 91 legacy L FWD by the way. anyways he says he can turn it with a screwdriver with the car off, and with the car on it doesnt spin so it mist be broken, but he cant figure out how to remove the speedometer gear from the tranny and 2 of the books he has dont get into detail on removing it?
can you please tell me how to do this if youve done it in the past or just know how to do it?

thanks

Try http://techinfo.subaru.com/html/index.jsp

it has service manuals and such, but it costs something like 30 bucks