I finally got time to replace the seals so here's a brief how to. It's quite similar to cheap motorcycle forks.
The main difference with cheap motorcycle forks is that the fork tops don’t unscrew like a motorbike – there’s a rubber cap that pulls off to reveal a white plastic insert that is fixed and doesn’t seem to have any way of removing. So there's no access at the top of the fork leg. The only way to disassemble is to undo the 8mm hex bolt in centre of the bottom of the lower fork leg.
Another difference is a circlip on the top of the stanchion above the steering clamp. This stops the forks from sliding out when unclamped. It’s not too difficult to unclip using a thumbnail. There's also a diameter change in the stanchion top that stops the fork stanchion from being pushed through the clamp beyond the design limit.
Another difference is the springs can’t easily be replaced because they are part of an assembled unit with the upper stanchion. When the hex bolt at the bottom of the lower for leg is undone (just like a motorcycle), the whole stanchion/spring/damper rod assembly slides out of the lower fork leg so the two are very easy to take apart, allowing easy access to the fork seal. The hex bolt is the 8mm and needs a few whacks with a hammer or impact driver to make it loose from the damper rod – that’s the same as a motorbike.
After replacing the seal and reassembling the lower fork leg with the stanchion assembly, fork oil has to be poured in slowly through the hole at the bottom of the fork leg where the 8mm hex bolt fits. You can't fill it from the top of the stanchion because of that white plastic plug at the top of that assembly. After filling, insert and tighten the 8mm bolt and it's done.
I used 120ml of ATF in each leg, and because there was really no damping before, it now feels heavily damped.
