Leaking shower faucet

I have a huge problem and hopefully someone here can help me and my dad solve it. I have a dual handle show faucet. From the faucet I get a constant stream of hot water, no matter how tight the hot/cold sides are. When the problem first began my dad relaced the whole fixture ( new faucet and handles). No help. Next we replaced the stems, they were wierd sized to begin with, but a local Hectors Hardware salesman helped us out. No Help. We replaced the seats. No Help. We replaced the plastic washers that sit on the stem. Actually, we replace them quite often because they actually dissapear as if there was never one there. I am at my witts end. I am sick of the gas and water bills being so high. Please help.

Replace the entire valve, body and all, not just the innards.

Pictures please!