The job starts, wheel off, cleaned the oil off the heat exchanger
Remove the rubber hose from the heat exchanger to get to the rear bolts. Remove the plug leads and wedge them out of the way - you can't get them back on in the wrong order as they are simply the order they come through the rubber body/tinware grommet. There are 11 x M6 Allen bolts on the lower covers. The heads on all of mine were corroded and caused some problems with a 5mm Allen key to remove. Thankfully they did all come undone. The cause was clearly that they had been removed previously - probably to replace the seal and most of the heads were butchered internally. I had temporarily replaced the bolts before starting the job, so that I knew they would all come undone - you can do most of them in advance without taking the wheel off.
Had to shorten a 5mm Allen key to get to the lower rear bolt
With all the bolts loose the cover just pops off. Cleaned the surface on the heads.
Installed the new seal in a new cover and bolted all new bolts up - tightening to 7 ftlbs - i.e. not very much. Refit the rubber heater hose and plug leads and it's job done.
New parts details:
Cover bolts (7ftlbs torque) M6 x 11 900 067 238 02 £0.42 each
Lower cover seals 993 105 135 02 £14
Lower cover OEM 993 105 16 07 £60.42
Labour £0 !