I use water in my brake. I'm using a current Magura HS33 rear, not had any problems with mine, I just give it a re-bleed now and again, but it's not that often probably 6 months or so. Rob Brodie has an Echo TR rear brake, and his leaks too, he's on his second, after sending his first back. As far as I'm aware he's gonna send his current one back, and possibly get the Echo CNC or a traditional Magura HS33. I've not used the Echo brakes, but after looking at Rob's it looks like there's a problem with the seals in the master cylinder where the lever piston pushes the fluid.