I would suggest using rubbing alcohol and a clean cloth or if they are in worse shape use a Bright Boy. Should get one of these anyway for regular cleaning once you lay track.
Walthers SceneMaster Bright Boy Cleaner Standard Grit Abrasive Track Toy https://www.amazon.com/dp/B000EXGNT0/ref=cm_sw_r_cp_api_i_0lddBb7PPF71P