Is there a Statute of Limitations when it comes to the Trustee collecting overpayment of DB to participants?

Sorry I don't know, but I suggest you try the litigation board and the distribution board.

A search on the Board will bring up quite a few old threads wherin this was discussed. There was also an Amtrack case on the issue.

Use the search feature at the top right of the page. Using the term "overpayment" should be sufficient.

There is no specific s/l for recovering excess benefits under ERISA. The period is determined by using the most relevent state law, e.g, contract, that applies. However since ERISA is a law in equity the plan admin. will have to identify the over payments in the participant's assets. If the participant has spent the overpayments there can be no recovery.