Many TDS 6XX scopes also had this problem. I run them through a dish washer first, then a Simple Green scrubbing followed by rinsing and blow dry using a compressor. After that I scrub 'em again with isopropyl alcohol, remove all the caps and replace with new ones. If it still doesn't pass it's diagnostics and SPC, start looking for open vias (usually black) and etches that are close to the areas where the worst of the leakage was.