I have a client who files an 1120S and wants to contribute to his solo 401k.  His W-2 has already been filed and there is no reference to his elective deferral on it.  Is this contribution something that would have needed to be declared with his payroll company before year end or can the W-2 be amended now?  He fired his payroll company and they're not willing to discuss this with him.  Is there any way to accomplish this without amending the W-2?  How would this be presented on the 1120S?  Appreciate all of your guidance.