My DC bass has D tuners. They work fine, and they can be disassembled easily for cleaning. They're not high-ratio (they're 14:1 or 15:1), but they work well enough. I see no reason to change them. I took them off and cleaned them because they were turning glitchily. Whatever lubricant was in them had gotten gummy.
My 56 has tuners that can't (as far as I can see) be disassembled for cleaning, but they've always worked fine. If some day they show signs of gumming up, I'll probably take one off and see if they come apart. They do have handy oiling holes, though.
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