Teachers, as defined in subdivision (3) of Section 16-25-1 or subsection (d) of Section 16-25-5, as amended may use their accrued sick leave, up to a maximum number of accrued sick leave days allowed by law, to be included as membership service in determining the total years of creditable service in the Teachers’ Retirement System of Alabama; provided, any teacher not authorized by law to receive sick leave may use any accrued sick leave provided by his or her employer, provided, that employer is lawfully empowered to grant such leave, which cannot be without pay; and provided further that the amount of such accrued leave shall not exceed the maximum number of accrued sick leave days allowed by law for a classroom teacher employed by a city or county board of education. Unused sick leave may be converted to membership service only for the purpose of applying for service retirement. The conversion shall not apply to eligibility for deferred retirement; provided that a person eligible for service retirement, if also eligible for disability retirement, may elect disability retirement and also receive credit for accumulated sick leave pursuant to this section. This section shall not be applicable to any person who is eligible to receive partial payment for accrued sick leave pursuant to Section 36-26-36.