I've already done the research. Here's a table of the different materials for cylinder seals and how they react to the fluid. Looking at the results, water has the most consistent performance.
There is another modification you should do to your hs-33, that will help it perform a little better, and last longer as well.
You will notice that the material that typically covers the TPA has been removed. We've had a lot of cases where the cylinder in the lever gets deformed (we verify with a caliper) due to the lever blade pressing against the removed area. It can also cause cracks in the lever body.
Whether your lever is bled with water or mineral oil, it still requires regular servicing. I've tried a lot brakes bled with oil that the rider claims to be functioning correctly, but it clearly is not. The only difference is that if you don't service a brake with oil, the brake only feels terrible and sluggish. Since the brake never worked that well with oil in the first place, riders don't notice.
we've had some good results using this for the winter seasons. It has very close viscosity to water, and doesn't freeze. It also has some lubricating features.
If you're not open to trying new things to improve the performance of the bike for trials, you probably should look at giving up your bike brand. I'll nominate frank as someone who is adequate for taking over :)