Sounds like the front trans pump, ZF's are famous for their pump failures. Try to set the proper level with the proper fluid and change out the filter by all means, you might get lucky. And be sure to follow the RAVE or other shop manual for refilling, you don't just dump in two gallons of fluid, there is a procedure for this.

'99 Disco II
'95 R.R.c. Lwb (Gone...)
'76 Series III Hybrid 109
'70 Rover 3500S