Thought I might share my gleaned info. for future use.
I had an odd and intermittent noise from F/N/S. Although it sounded nothing like the classic C/V grumble/clicking, the replacement driveshaft cured the problem.
Problems on the way included identifying the correct shaft. The EGS6 box is a 6 speed manual - or auto- according to which hymn sheet your on. The part no. taken from Citroen Service Box then translates into multiple choice by suppliers.
The answer was to find a supplier that could cross ref. the vin. I found Mister-auto very helpful and competitive.
The box has no oil fill/level plug. It has to be drained completely from the bottom ( 8mm square drain key) and then refilled through the vent at the top of the box. The vent cover just pops off and can be got at without removing the battery
The exact amount needs to be put in. Gear oil 2.1 ltrs 75/80 fully synth. gl4/5
As a 'get out of jail' card- about 750 ml. remains in the box when the shafts are pulled. But this flags up other issues- the correct oil level is way above the oil seal. So their condition is critical.
Finally- the gear oil that I drained out seemed to be really thin. Like ATF automatic gear box fluid!!! I shall never know.