I've got a 91 legacy automatic and the speedometer cable recently started leaking. I traced it to the fitting on the tranny and replaced this, but broke a nylon gear inside the tranny connecting to the speedo shaft. I changed the differential fluid and indeed pulled out a piece of the gear. How bad is it? How big of job is it to repair the gear? If I drive without the speedometer will this hurt the car? The check engine light comes on and a code flashes at start-up.

Yeah, the VSS is shot. Sorry, but that gear is absolutely necessary and it requires dropping the tranny to fix it.