I've got the early Keisler hydraulic setup without bleeder valve. It can take quite a few pumps to get it primed but once working it has been trouble free. Newer versions do have the bleed valve.

It sounds to me like a heat problem boiling the fluid. Does the line run close to the manifold/headers? Maybe re-routing or insulating the line would help. As far as fluid goes, they are all "synthetic" in some sense and mixable. DOT 4 has a higher boil point than DOT3 and DOT5 is higher yet. I have run DOT3 or 4 conventional fluid without issue. With a possible heat issue, maybe run DOT4. I am not sure these systems respond well to silicone DOT5 so I wouldn't recommend it.