I have an old delta two handled tub faucet. The cold water side leaks. What can I do?

I have an OLD delta two handled tub faucet. The cold water side is dripping. How do I fix it?

Turn off water, remove handle and trim. Remove faucet stem. The stem should have a bonnet nut around it that prevents water from leaking around the stem. Behind that you should see the shoulders of the stem. That is what you want to remove.
You will need a set of tub faucet wrenches (cheap looking sockets) and a seat wrench. Remove stem and seat. The seat is the thing that the rubber washer on the end of the stem presses against to shut the water off.
Remove seat and take with you to hardware store to get replacement.