I've had this J-60 for almost 20 years. It sounds crazy i know. I got it in a trade back when these were practically free. It was an "i'll throw in this old keyboard" type of deal. So it's always been happy except for 3 or 4 sliders that were dry and got damaged by someone forcing them to move. It doesn't look like anything was even spilled in there! I located some replacements but upon further inspection i found i could refurbish most of the original ones. This required desoldering them from the main board and disassembling them by un-pinching the tabs on the metal housing to get at the innards. i then flattened out the bent metal runners that had been mangled over the years. After cleaning the parts and adding some new grease i reassembled them for reinstallation.
Here's some pics of the process...
Photos courtesy of J-poo