The Moondrop slider is precisely machined to fit perfectly on the tube and to create the super smooth drop. If the tube or slider gets dirty or some tiny dust gets between the slider and tube it could mess up the sliding smoothness. If that happens you should just clean the Moondrop. First you should reassemble it:
For the ''Lunar'' and ''Earth'' versions: clean both -slider and tube with sponge and soapy water, then dry them with cotton cloth. This will insure that there is no dust and the slider and tube both are absolutely smooth. You can also wash the ''Lunar'' and ''Earth'' Moondrops without reassembly. After cleaning you should assamble the Moondrop and move the slider intensely for about 20 seconds before start using it again.
For the ''Mars'' version: clean the aluminium tube with sponge and soapy water, then dry it with cotton cloth. Leave the copper slider dry and just polish it with dry cotton cloth. Copper oxidizes very easily so we recommend not to make it wet. Than you should assamble the Moondrop again and move the slider intensely for about 20 seconds. This should make the Moondrop work perfectly smooth again.