I should know this by heart, but I still draw a blank...unless it was the first race with outboard fronts on the 711?
Ronnie had a bad brake-shaft failure in Frank Williams' private 711 at the Race of Champions at Brands and I know he demanded Robin Herd to rebuild the factory cars with outboard fronts after that.
Poor Frank probably had to soldier on with inboards, unless he paid MrM an unscrupulous amount to have the rebuild.
As a side note, Frank thought he had bought a finished car, but the 711 was delivered IKEA-style.