Scooterotica

Use clear hose as the reservoir, then you can see how much fluid you have.

Would something like this do?

or as Frautzi says, a length of non reactive clear tubing. Or fab one up from a length of ally tube. Or some of the ones on ebay (master cylinder reservoirs) may just fit up inside the headset itself, make ckecking levels much easier. Or this from ebay (brembo brakes), would fit snuggly inside?

you can't help noticing that a new part is less than a £10er, but some S/H part is over £40.

Clear hose

I'm planning to drill and tap 2 mounting holes just under the frame to mount mine. I might also put on a ali guard around it for protection