400ml came out of each leg, I put in 425ml of Silkolene 10w in each side as my preload was on max so wanted to reduce air gap and was getting chatter on the brakes.

Now I have preload on 2nd line from minimum and wound the damping off 3/4 a turn as smaller air gap increases compression as well as pre load. Front is now as good as I can get without new springs or cartridges.

Unless you are at max pre load I would go no more than 410ml max. If you have no handling or adjustment issues stick to 400ml.