The rocker cover gasket in something like a nova, which is probably the last one I have replaced, is a simple job, as the camshaft is at the top of the engine, and it takes about 10 minutes.
The impreza is not so simple, as with a box engine the camshafts are down at the side. So I stripped back the airbox, and the boost solenoid assembly to give me space and eventually managed to get the six bolts and cover off. It took ages to clean the seal as the old rubber gasket had disintegrated and stuck itself all over the place.
Placing the new gasket, and getting the cover back on was a breeze, and I then screwed everything back together, and as always was pleased when I turned the key and heard the engine start. Now all that remains to be seen is if the oil leak has actually gone, and if that is the last one!