Too much for me was when it started getting more difficult to held a precise straight line and steering effort increased at speed, and the leak got bad enough to motivate me. Mine was a packing gland style. I'd imagine too much slop in a seal style could prematurely wear or damage the seals.

FWIW the big MC rudder cost me $716 all said and done, plus $131 for a new helm, cable, and misc. bits. Worth it to have a dry bilge and smooth, precise, easy steering.