If any person who hereafter becomes a county employe and thereafter ceases to be a county employe and his or her contributions as paid into the retirement fund are refunded by the board, is reemployed by the county or county institution district and he or she desires to be given credit for previous service as a county employe, he or she shall make payment in full of the amount refunded, with interest at the legal rate, the said interest to be computed from the date of refund to the date of repayment. Both principal and interest shall be paid into the retirement fund at one time and in one amount, or, upon approval of the board both principal and interest shall be consolidated into one amount and paid in twenty-four or less equal monthly installments, plus interest payments on monthly balances. Whenever the time for payment in full has been extended for an additional period of one year the principal and interest may be paid in a total of not more than thirty-six equal monthly installments. Full payment thereof shall be a condition precedent to the county employe being eligible to receive the benefits of the retirement allowance plus a service increment, if any. Such county employe shall make monthly payments into the retirement fund in accordance with the provisions of section 1708. Any person who is a county employe on the effective date of this act may make payments into the retirement fund which shall cover a period of time within which such person was a county employe but was not a member of the retirement system because such membership was not compulsory.
16 P.S. § 4715