Any civil service employee of the state of Washington or of any political subdivision thereof who is on leave of absence by reason of having been elected or appointed to an elective office shall be preserved in his or her civil service status, his or her seniority, rank and retirement rights so long as he or she regularly continues to make the usual contribution incident to the retention of such beneficial rights as if he or she were not on leave of absence: PROVIDED, That such contributions being made shall be based on the rank at the time of taking such leave of absence.