I would replace the leaking strut (only that strut) and the accumulators (gas spheres). The accumulators are responsible for the shock absorbing. And use the fluid as printed on the reservoir cap. Often, signs of bad spheres are hard rear rides and low reservior fluid levels (because the fluid has leaked internally to the gas chambers).
I would leave the front shocks alone at this mileage for now, if your wagon 4Matic. If not, take care of the rear first to see if you are satisfied with the ride then decide if to do the front shocks.
I would leave the front shocks alone at this mileage for now, if your wagon 4Matic. If not, take care of the rear first to see if you are satisfied with the ride then decide if to do the front shocks.