Shower faucet leaks after replacing entire stem assembly

Motorapido

Amateur plumber baffled by leaking shower faucet. House is 90 years old. I've owned it 3 years and this is my first repair on the shower. This is a four-handle setup, with no diverter. Lower two handles turn the water on and off for the tub spigot. Upper two handles control water to shower. The rough-in body looks very ancient when I view it through the service access door. Shower is surrounded with concrete set with original tiles. Anyway, after replacing the flat rubber washer to attempt to fix the leak, the leak continued. The stem assembly does not have a removable seat like I have often replaced/repaired/dressed before. I photographed the stem assembly and sent photos and dimensions to Chicago Faucet Shop, when my local, huge to-the-trade plumbing supply outfit could not visually identify the stem assembly. Chicago Faucet sold me an American Standard stem assembly AMERICAN STANDARD - 16762-0200 as the replacement part. The old stem and new stem were visually almost identical in every way. The only difference on the new stem assembly is that at the bottom of the brass cylinder that the stem screws down into, on the exterior of that cylinder, there is a groove machined into the brass and a rubber o-ring. The stem assembly I took out did not have a machined groove or o-ring at the base of the brass cylinder.

I installed the new AMERICAN STANDARD - 16762-0200 stem assembly, turned the water back on, and the leak through the spigot continued, same as with the old stem assembly. The new stem assembly came with a new gasket. I made sure the screw holding the gasket was greased and tightly turned down.
Could it be possible that the ancient rough in assembly has a crack in its body or some other type of flaw that is allowing water to escape? There is no water leaking around the stem. It's just that with the handle turned tightly off, a very fine stream of water continues to come out of the spigot. It is more than a drip. A very tiny stream of water. I have attached a photo of the old stem assembly. Any ideas what could be the issue? You can see in the pic that the washer screws down flush with the interior base of the brass cylinder, and that entire assembly screws into the rough in assembly.

Intplm.

You ask if there could be some type of flaw? I am thinking that the shower valve body has a deformity that does not allow for the new parts to fit as intended. Over time, with water running through a valve, small areas of erosion take place. Your shower valve more then likely has that issue.

This valve is likely original to the house? Ninety years old?

Before giving up on it , try cleaning the seats again.
And flush the hole repair area with water.

Are you sure there are NO removable seats on this valve?

Clean every part that touches water. Water is tough! It will always find a week spot to flow out from.

Lyle {pheloa} Carter

In your photo it looks like you've reused the old bonnet (the threaded part on top). When I've repaired these in the past all the ed new parts were needed.

Alan (California Radiant) Forbes

There are two places that seal water on your stems. The barrel (the part with the new o-ring) seals against the seat in the valve body and the rubber bibb washer seals against the seat in the barrel. Either one of them could be leaking, but since you replaced both the stem and barrel, it should have taken care of the problem.

Did you replace both hot and cold assemblies?

BTW, nice floor tile!

Motorapido

I re-used the bonnet because the bonnet on the replacement stem assembly didn't have a threaded top that is necessary for attaching the escutcheons. The old bonnet sealed the stem perfectly.

Motorapido

OK, friends. Confession time. Like a dumb idiot, I did not realize that the other stem assembly was also leaking a little. I had mistakenly diagnosed the leak as coming from just one of the two when I found that by tightening the stem that I suspected as the leaker VERY tight, the leak slowed. I solved the problem when I replaced the other stem assembly too, and now I have a completely leak/drip/drizzle free shower. Live and learn. Meanwhile, I highly recommend Chicago Faucet Shoppe. I spoke to an employee who handles phone questions and he is a highly experienced plumber, and was very helpful in identifying the stem assembly I needed and making helpful suggestions on the installation. Their price was significantly lower than other suppliers of the same stem assembly and shipping to Pennsylvania was very fast. Great supplier.

Intplm.

Good to hear your done, no matter how it went it's always nice to hear a successful ending.
Very happy to hear this too cause I was hoping you would not need to replace that shower valve. That would have been a shame considering the four handles. Heck! I hope, and you just might get another 90 years out of it.

P.S. Thanks for the tip about "Chicago Faucet Shoppe" I'm always looking for places like this for parts in this situation. I will be checking them out.