If it is an UGLY its filled with potting material (epoxy), which is the hard putty looking stuff, and cannot be opened.
Yes clean the jacks with contact cleaner or denatured alcohol. Use Bob's suggestion and apply it to a miniplug, then use that to clean the contacts by working it in/out and spinning it around. If that's not enough I've sprayed a quick spritz of Caig Deoxit directly into the jacks of my UGLYs using the little red tube without problems when the contact intermittency problems from accumulated dirt and grunge were particularly bad.