Hey, mine is a bit worn so I want to change it, can I use anything from ebay like this:

http://www.ebay.co.uk/itm/1pcs-Front-Brake-Clutch-Cylinder-Fluid-Oil-Reservoir-for-YAMAHA-YZF-R6-05-13-/321274143701?hash=item4acd6e63d5:g:dWcAAOxyRhBSqr5w

Should be fine, the reservoir level doesn't go down much even, with pad wear, on twin disc set-ups. My only advice would be to inspect the quality of it before fitting. It should be fine though, it is only a reservoir.

Okay thanks!