Right, been a wee while but bought another 2nd hand OMP strut brace on Sunday as I was assured it had come off a mk2 16v.
Still the same issues

Why is nothing ever straight forward on my car?
Had a thought, and looking at the pic's kindly supplied by Adam again, I'm
fairly sure I have a spare reservoir from an A4 that is squatter and fatter but has same size lid. That's the theory so will see if I can trial fit it tomorrow after work.
Will put up pics if it works.