Seals have two enemies, pressure and soap. Pressure can penetrate to some extent. Soapy water can penetrate even more with its lack of surface tension. I spray non-seal areas with a hose and wipe as necessary. Sealed areas have dirt wiped off, wet if necessary. I always remove the chain (use a quick-link) and clean the gear teeth (use anything but a file). The chain is soaked in a coffee can with the cleaner-of-the-day green, orange, or solvent. The can is shaken and drained. Repeat if the drain solution is dirty. Soak in denatured alcohol and hang to dry. Measure the full length for wear while it hangs.