Driveshaft seal

My 2005 380 GT (157,000km) needs a new driveshaft seal (driver's side). Transmission fluid was replaced recently, so reluctant to replace more than I need to in order to fit new seal. Does anyone know how much fluid one needs to drain to remove shaft.

My car has reached that point in its life where a few things need to be done. Have just fitted new rocker cover gaskets. There was a little oil in each of the spark plug tubes. Whilst the intake plenum was off, fitted new iridium plugs (did all 6). Of course the old rocker cover gaskets were a pain to remove. I tried everything and learned that running a stanley knife between the gasket and the cover on both sides of the gasket (cut all the way through) enabled me to then lever the gasket out using a screw drive, whilst pulling on the gasket end with pliers.