I have rebuilt the valve on my three handle shower stems and they still leak cold water out of the spout. I switched the cold with the hots stem and it continues to leak cold water. Is it possible that the valve body on the cold side in deterated? If so can it be replaired without replacing the body?
Thank you,

Did you replace the seats when you replace the washers?

Yes

If you switched stems and it continues to leak on the cold side, that indicates to me that the seat was not properly installed. Seats are are the only part of a valve body that wear.

Remove and reinstall the seats. Put the seat that is presently in the cold side in the hot side. If that solves the problem it was a installation problem. If the leak moves to the hot side the seat is defective.

If the cold continues to leak post back.

When installing valve stems always install with the valve in the open position.