As in they want to sell you the full axle? There's a lot of work in replacing a R&P, and skilled as well since you have to get the parameters right (like backlash and the other two I can't remember), so by replacing the whole axle, you could probably save in labour the extra you pay in part cost. Provided there's a warranty of some form on the axle to protect against "the LSD is stuffed" of course. Many wreckers will warrant certain parts. Something to think about.