Agreed - a weird goo to use here, but also bear in mind I had a manual Landy Discovery that use watery ATF fluid in the main box....
and that thing weighed nearly 3 tonnes.

A Ford Capri 2.0 litre engined I had years ago used EP 90 - like thick syrup.... doubt I'd get the XF box to engage with this

I tried some other thicker fluids in another landy, and destroyed the transmission in under 1,000 miles !!!
Could barely get it into gear with the thick stuff in it.

The fact that it's a Merc box and these mechanics often survive 400,000 miles and more - I'm gonna believe the manufacturer lol

Grant B