(a) A member who has not retired may establish service credit in the retirement system for any calendar year during which the member:
(1) held an office included in the membership of the retirement system; or
(2) was eligible to take the oath for an office included in the membership of the retirement system.
(b) A member may establish service credit under this section by depositing with the retirement system a contribution computed for each month of credit claimed at the rate of six percent of the member's current monthly salary, plus, if the member does not establish credit before the first anniversary of the date of first eligibility, interest computed on the basis of the state fiscal year at an annual rate of 10 percent from the date of first eligibility to the date of deposit.