Heavy rear transmission vibration at 70mph or 2500rpm

Hi guys

This is my first post on here,
I have an 07 freelander 2 GS, over the last 12months, a heavy vibration has started in the transmission. It happens at 60 - 70mph in sixth at just around 2000rpm. It gradually builds, but it does not subside if you go slower or faster, you need to stop completely then start again.
When it’s at its worst you can smell transmission oil, but you can see no fresh oil around diff or gear box outputs.
Does any one have any ideas ????? Help

When was the last time you had the Haldex/rear diff serviced/flushed?

Check the propshaft centre support bearing. It's not uncommon for the rubber mount that holds the bearing to disintegrate, causing the shaft to run off centre.