(a) If an employee who has received a separation benefit subsequently becomes a participating employee, and renders at least 2 years of contributing service from the date of such re-entry, he may pay to the fund the amount of the separation benefit, plus interest at the effective rate for each year from the date of payment of the separation benefit to the date of repayment. Upon payment his creditable service shall be reinstated and the payment shall be credited to his account as normal contributions. Application must be received by the Board while the employee is an active participant in the Fund or a reciprocal retirement system. Payment must be received while the member is an active participant, except that one payment will be permitted after termination of participation in the Fund or a reciprocal retirement system.
     (b) Beginning July 1, 2004, the requirement of returning to service for at least 2 years does not apply to persons who return to service as a sheriff’s law enforcement employee. This subsection applies only to persons in service on or after July 1, 2004. In the case of such a person who begins to receive a retirement annuity before the effective date of this amendatory Act of the 94th General Assembly, the annuity shall be recalculated prospectively to reflect any credits reinstated as a result of this subsection, with the resulting increase in annuity beginning to accrue on the first annuity payment date following the effective date of this amendatory Act, but not earlier than the date the repayment is received by the Fund.