(1) The portion of service credit not earned during a paid sabbatical leave granted after July 1, 1966, may be purchased if the member makes member contributions on the difference between the partial salary paid and the salary which would have been paid if the paid sabbatical leave had not been taken.
(2) Such member contributions made pursuant to the provisions of subsection (1) of this section may be made concurrently with member contributions on the partial salary paid for such sabbatical leave or after the sabbatical leave has ended at the applicable rate of member contributions pursuant to section 24-51-401 (1.7), plus interest from the date the sabbatical leave began until such purchase is complete.