Been there done that. The water can be leaking 'down' to the valves making it look like you just needed the valve replacement.
I had the valves only to still have sewage dripping.:S
What it ended up being:
I had 'hairline' cracks
around where the four screws hold the attachment
. THAT is where the water can be coming from.
They are nearly impossible to see them but they are enough to leak water.
Repair guy says he sees this a lot. The sewage assembly hangs suspended and moves and takes a beating when going down the road.
Hairline stress cracks happen around where the screws go in.
During the repair one was stressed with several hairline cracks it broke off. Sadly this is a molded part of the lead pipe, and has to be cut off, replaced and repaired with a rubber clamp just like home plumbing.
So check with a flashlight around where the screws go in for hairline cracks.
Hope this helps.
