Replaced shower valves and seat - still leaks

I have an older 3-handle system in my bathroom shower: hot, diverter, cold. The water was never quite shutting off all the way - more than a drip, slightly less than a constrant stream. I took the handles off, pulled the valve stem out and took it to Home Depot and matched it perfectly. I took them home and removed the valve seat, put the new valve seat in (I couldn't get the hot water valve seat out but it looked pretty good so I left it), put the new valve stems/bodies in and there's no change. I turned the water on to each handle one at a time and they both still leak. If it was just the one with the old valve seat I could maybe see it but the new one is just as bad.
Any ideas on :
1. what I might've done wrong (going to HD notwithstanding] 2. how to fix ?
Thanks, p@
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p@ wrote:

Did you apply sealant to the seat threads? If not, even a perfect seat will leak. I don't like Teflon tape in this application; too hard to wrap and be sure it's on there. A good pipe dope is better.
The hot side is the seat that usually goes; I would change it too,.
Jim
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Aha. I'll get some pipe dope and apply. I'll work harder to get the hot side seat out.
Thanks
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I once had a shower valve with a channel corroded through the seat threads. It leaked with new seat and washer but I was able to seal it with some real thick sealer. Don Young

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You didn't say where it leaks. If it drips from the spout then as Jim suggested, seal the threads on the seat. We are also assuming there is a washer on the end of the new stem.
Now, if the leak is from behind the handle then you have a problem with the packing. You can get some graphite packing and wrap the stem and then tighten up the stem nut.

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It's not from behind the handle - it's down the spout. Yes, the stem came with a new washer.
Thanks.

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