Gently tap out the main oil seal together with the metal spacer using a suitably-sized socket or drift.

If you plan to replace the main output bearing, you can also tap this out with a socket or drift; it should come out easily.

Drift out the steel plug covering the layshaft bush and drift the bearing out (if it hasn't fallen out already).

Unscrew the gear selector pivot shaft

Unscrew the detent plunger housing bolt.

Note this bolt may be incredibly tight. If it's stuck, apply a bit of gentle heat to the casing and use a power bar and a good-quality wall-drive 21mm socket to remove it.

There's no need to remove the gear selector bush, as it's unlikely to be worn.

Wash the casing out with paraffin or degreaser.