We recently discovered that our PA40 Retirement Action has changed since our initial set up vs. our PA40 Separation action.
PA40 Separation allows us to delimit recurring payment/deduction (IT0014)
PA40 Retirement does not bring up IT0014 but it should
Where would I begin to trouble shoot? Dynamic actions, user exit...
Also, any idea service pack may have caused the issue and why?
You don't mention what release you're on, but in any case I can't think of anything in an upgrade or application of a support pack that would have cause any change to the Retirement Action. Sometimes if you are using the SAP standard action rather than copying one to your own name range, it might be possible values could change, but I doubt this is the case in this instance.
Things to check would be:
Action configuration for your Retirement Action, compared to your Leaver Action - work your way through the IMG nodes under Personnel Administration > Customizing Procedures > Actions.
Pay particular attention to: User Group assignment - is it possible the user running the action does not have the correct UGR parameter set in SU3/SU01? This could lead to different infotypes being presented to the user even though the configuration hasn't changed.
Also look at the Infogroup configuration in V_T588D to double check IT0014 is included for the retirement action; assuming yes (from what you say, i.e. that it was working previously), check the Operation assigned. For delimiting, this would be LIS9. For the infotype to be presented for delimiting during the Action, the employee would have to have an existing IT0014 as part of their master data or else the IT would be skipped during the action.
Failing that, as you said, there is a chance a dynamic action or user exit is being triggered that may not be an obvious part of the Actions configuration. You should be able to check this & may need to get help from an ABAP-er to do this.