Something I used (probably not a good idea for circuitry) on plastic parts was a degreaser. Specifically I used Super Clean Tough Task Cleaner Degreaser from Casey's (think 7-11, Gas 'n Stop, etc.). (my brother smokes like a damn chimney)
When I've used it on plastic, glass, non-porous surfaces that damn nicotine comes right off. Your paper towel will be a disguisting yellowy-brown. It smells exactly like 409 cleaner, feels like 409, looks like 409, makes you choke like 409, etc. So 409 might work just as well.
Never checked for smell beforehand but afterwards there wasn't any. Just be sure to RINSE, RINSE, RINSE. I don't use it on anything I can't hold under warm running water and rub with a clean rag/paper towel. It takes quite a lot to rinse the degreaser off. (which may mean there is more left to clean)
** must warn you, I've only once used the degreaser on an ink surface. i.e. the keyboard back-plate on a HP-91/97, for example, where the yellow nomenclature is. The yellow lettering looked very solid and I only sprayed and immediately rinsed. I have used similar cleaners (Mean Green?) on keys of a HP-46 (removed & washed each key cap) and in a few light rubs the cleaner started taking the colored lettering right off. So I make a point to never rub on ink-printed nomenclature. Use a q-tip & go around it. Spray on the lettering and then immediately hold under water. Then PAT the lettered area dry.
Maybe the colored lettering on a 46 versus newer items is different, but never trusted the cleaner subsequently. i.e. the coloring on the 46 appeared to hold, then in about 1/2 a wipe most of it was suddenly gone.
But never had any problem using the degreaser on a case and rubbing on it with a rag.
Calculator from a smoking environment: What is to be done?
