I would say NicoVolta 's "magic brush treatment" https://pinside.com/pinball/forum/topic/nics-american-pinball-tour-aka-im-coming-to-fix-your-games/page/44#post-4452119
The unit I believe you are speaking of would be the "score motor"
will be scary & tedious at first but will get easier as you get more comfortable doing it ( ONE stack at a time !!! )
rubbing alcohol should clean up the WD-40 residue
some other helpful tips here: http://www.pinrepair.com/em/index3.htm#motor