ZF Gearbox fluid and filter change

[ptjs1]

At 120k miles, I'm just about to change my fluid and filter for teh second time, having done it previously at 75k.

This time I'm using an aftermarket sump / filter, having been advised by Bristol Transmissions that it has a better seal than the original ZF fitment.

I'm going to use Millers ATF DM fluid this time, having read good comments from owners on another Jaguar site. I can buy the fluid in 5 litre containers at a good price. I don't particularly want to have to buy a 6th litre as the 1 litre container is not such an attractive price.

My question is, do I really need 6 litres for a change (last time I did use 6 litres of Shell M1375.4)? And if so, is it a bad move to mix a spare 1 litre container of M1375.4 that I have with the Millers ATF DM?

Any thoughts appreciated.

Paul