That washer in the upper part of the housing is a part of the old shift rod seal.
Pull it away and clean the wall of the seal seat with fine sandpaper.
Lube the new seal with gear oil and push it in with a suitable socket from upper part of the gear housing.
Be careful when start pushing the new seal in, check so it would go in straight.
When reassemble lube the shift rod with gear oil cause the new seal will fit and seal more than snug so the shifting can be hard in the begining.
Pull it away and clean the wall of the seal seat with fine sandpaper.
Lube the new seal with gear oil and push it in with a suitable socket from upper part of the gear housing.
Be careful when start pushing the new seal in, check so it would go in straight.
When reassemble lube the shift rod with gear oil cause the new seal will fit and seal more than snug so the shifting can be hard in the begining.