I'd bite the bullet and pay the ?66.55 if I were you (although I dunno what their shipping cost is). At least you know you're getting something that'll work, rather than going through the process of re-inventing one.
Actually, looking at the parts drawing, it appears to be little more than a short piece of tube with an external thread each end. So it probably wouldn't be too difficult to make one on a lathe. Transparent acrylic plastic comes in round bar or tube form, and I think it's OK with brake fluid.