> Medicare tax is uncapped as of several years ago, I thought?

Yes, it is, but it's taxed far too low relative to its spending given the current healthcare cost structure. As a result, only half of the Medicare costs are funded by the Medicare Trust Fund, the other half is deficit funded.

In other words, unlike the Social Security tax, Medicare isn't self-funding from the Medicare tax because it's set artificially low (or healthcare costs are too high, if you prefer).