Oil leaking from the geabox to the drum brake

Since I bought the bike the back brake has always been fairly useless. At first I put this down to the Gazelles odd combined brake linkage - both brakes are activated together regardless of which lever is pulled on the handle bars. Because of this linkage tuning the biting point of both the front and rear brakes to be in sync is tricky. However it was always bad even after carefully adjusting it.

It is a pain to look inside the rear drum brake as lots of parts have to be removed to get to it so I haven't been able to regularly look inside but began to notice it is often oily in the brake drum.

For a while my suspicion was that oil was leaking through the bearing race. However after a few rebuilds of the gearbox and making sure the bearings weren't leaking oil thsi seeemd less likely.

Eventually after an oil change in the gearbox and that the wheel was left out before immediately going back on the bike I noticed that oil was seeping through the joint between the gearbox end cap and the brake drum.

The end cap is pressed on with a splined interference fit. It took some persistent and force full knocks to remove it.

The inside of the drum brake