Couldn't find an oil height / amount – so did some experimenting.. too much oil just means you don't get full travel. no effect on the damping (i.e. still none) – there's a slight notch on my 'Glide ring' – not sure if I put it there taking the damper out or it was there in the first place – could explain it. Ordering the damper service kit with a new glide ring – so will see if that makes any difference…
Both damper adjustments seem to be working mechanically (i.e. I can see the low speed valve open and close, and the high speed spring getting stiffer – so it must be a leak caused by the glide ring – or some other sort of fault with the damper..