How to care for hard rubber
Long exposure to direct sunlight is bad for the pen as it will cause slight discoloration
Do not use hot water or soak the pen in water.
Cleaning the exterior:
if ink stained, use a slightly damp cloth to wipe the exterior and use a dry towel to wipe it dry.
else, use a dry micro-fiber cloth to clean the exterior.
Polishing the exterior:
Polish with 12000 micromesh seems to give the best results, simichrome/autosol/micro-gloss works as well, but use with caution as discoloration might occur if used in excess.
Oxidation due to sunlight & water.
If the pen has been over exposed to sunlight and then moisture, the hard rubber might oxidize and form a discolored layer on top. this can appear as beige,olive green or brown.
If your pen has chased patterns (or any patterns where there is a difference in surface level) like BHCR, the best option is to dye the pen black with pensbury pen potion #9.
Otherwise the oxidation can be removed by using micromesh or simichrome/autosol/micro-gloss