(1) A dual member may combine service in all systems for the purpose of:
(a) Determining the member's eligibility to receive a service retirement allowance; and
(2) A dual member who is eligible to retire under any system may elect to retire from all the member's systems and to receive service retirement allowances calculated as provided in this section. Each system shall calculate the allowance using its own criteria except that the member shall be allowed to substitute the member's base salary from any system as the compensation used in calculating the allowance.
(3) The service retirement allowances from a system which, but for this section, would not be allowed to be paid at this date based on the dual member's age may be received immediately or deferred to a later date. The allowances shall be actuarially adjusted from the earliest age upon which the combined service would have made such dual member eligible in that system.
(4) The service retirement eligibility requirements of RCW
41.40.180 shall apply to any dual member whose prior system is plan 1 of the public employees' retirement system established under chapter
41.40 RCW.