For periods of employment as a member of the Teachers’ Retirement System or the Teachers’ Pension System for which the member is not otherwise entitled to service credit, a member of the Teachers’ Pension System may purchase credit for eligibility service as provided in this section. The total amount of service credit in the Teachers’ Retirement System or Teachers’ Pension System that a member may purchase under this section and § 23-308 of this subtitle may not exceed 10 years. A member who purchases service credit under this section may not purchase service credit for any period of employment during which the member participated in the optional retirement program. To purchase service credit under this section, a member must: complete a claim for the service credit and file it with the Board of Trustees on the form that the Board of Trustees provides; and pay to the Board of Trustees an amount equal to one-half of the annuity reserve and one-half of the pension reserve required to fund the additional allowance.