It's a good starting point to see what is worn out in there. There are those who experience leaking at the caliper end ( it's happened to me as well ), but the inconsistency issues stem from the lever.
The plastic piston in your lever will likely show scuffing on the largest diameters that contact the lever bore. The scuffing will be uneven as well due to the piston seeing side loads from the design of the servowave movement combined with the minimal amount of "bearing land".
U-cup seals on the piston are likely tired, and can't compensate for extra radial movement of the piston in the lever bore.
The lever bore may be scored at worst - slightly worn at best. While any anodizing may have been light to non-existant; I don't think this is necessarily the major culprit. The fluid can become discolored, but we are looking for a wholesale leak-by of the seal. Every single Shimano lever I have put miles on exhibits the same behavior. Inner seal will not allow line pressure to build, and maintain that pressure, when it passes the timing port in the lever. Outer seal also allows fluid out, and the outside world dirt in. The outside of my lever shouldn't be damp all the time.
What can you do? Don't invest too much time in surgery, unless you really like experimenting. Shimano went cheap and disposable with the design. Also the bushing for the lever pivot is just a tiny bit of plastic (usually integrated into the plastic track for the servowave mechanism. Lever play on every one I own. I'll wear these out even before the internal issues develop. It's kinda sad. I hate throwing things out.
-You can rob the piston and seals from another lever. The lower the use the better. Low level series levers like some of the Deore even have the MC piston as aluminum. This may help, but only will buy you time.
-Mad scientist route. There are small flex hones made for 10mm bores. Refinish the bore --> Measurements (ugg this is a pain) --> Source new seals: example https://www.mfpseals.com/content/mfp-seals-engineering-guide-vol-3 ( this is way too much bother ) --> ??? --> I can tell you this does not end with profit.
-Best fix. Get a brand new lever. Get the usable lifespan out of it.
-Best plan. Change to another brand.
Already wrote too much. It's too bad Cura 4's aren't working out for you. I'm 4 months in on mine with no issues.
The plastic piston in your lever will likely show scuffing on the largest diameters that contact the lever bore. The scuffing will be uneven as well due to the piston seeing side loads from the design of the servowave movement combined with the minimal amount of "bearing land".
U-cup seals on the piston are likely tired, and can't compensate for extra radial movement of the piston in the lever bore.
The lever bore may be scored at worst - slightly worn at best. While any anodizing may have been light to non-existant; I don't think this is necessarily the major culprit. The fluid can become discolored, but we are looking for a wholesale leak-by of the seal. Every single Shimano lever I have put miles on exhibits the same behavior. Inner seal will not allow line pressure to build, and maintain that pressure, when it passes the timing port in the lever. Outer seal also allows fluid out, and the outside world dirt in. The outside of my lever shouldn't be damp all the time.
What can you do? Don't invest too much time in surgery, unless you really like experimenting. Shimano went cheap and disposable with the design. Also the bushing for the lever pivot is just a tiny bit of plastic (usually integrated into the plastic track for the servowave mechanism. Lever play on every one I own. I'll wear these out even before the internal issues develop. It's kinda sad. I hate throwing things out.
-You can rob the piston and seals from another lever. The lower the use the better. Low level series levers like some of the Deore even have the MC piston as aluminum. This may help, but only will buy you time.
-Mad scientist route. There are small flex hones made for 10mm bores. Refinish the bore --> Measurements (ugg this is a pain) --> Source new seals: example https://www.mfpseals.com/content/mfp-seals-engineering-guide-vol-3 ( this is way too much bother ) --> ??? --> I can tell you this does not end with profit.
-Best fix. Get a brand new lever. Get the usable lifespan out of it.
-Best plan. Change to another brand.
Already wrote too much. It's too bad Cura 4's aren't working out for you. I'm 4 months in on mine with no issues.
No. Why?