washer leaves water after wash/drain, anywhere from level with top of sump to 1/2" above bottom of pan, since I only need to wash every 5 days or so it often ends up stinky... I've had it over 10 years, seems to have developed the problem in the past year.

Everything else seems to be normal, no unusual noises, can see a good stream of water pumping into the disposal, no problem getting the dishes clean but the fine filter at the back of the washer collects lots of fine crud (on check valve side) that doesn't flush out (is it supposed to?) even after replacing the check valve and cleaning everything out, seems I now have to remove/clean it every 3-4 loads or scrub the dishes clean before loading, which makes no sense, but seems is what most people typically do to avoid food particles ending up on the clean dishes, which also happens but less so since replacing the check valve.

I've read other discussions on the topic, checked the sump and elsewhere for obstructions, screens and anywhere else I could think of, replaced the check valve (it was all torn up after 10+ years,) have to check the solenoid, but not sure what else. As shredded as the checkvalve was, i'm wondering if the pump impeller might be trashed and part of the problem too, replacing that and seal seems next obvious step.

Also wondering what is "normal" residual water level in the sump since it obviously can't drain everything having to pump uphill to the disposal and doesn't have an air gap but does have the high loop in the drain line.

Now that i've tried fill/drain a number of times I see what looks like fine metal particles (like black sand) in the bottom of the tub along with a rust spot where some has been sitting for a while... and I noticed that the NEW piston jams shut every time I fill/drain, need to remove it to release, won't go down with finger pressure.
Help?

Turns out it's most likely the check valve flapper that has failed, on the outlet side of the pump assembly, hope this helps others that don't get a response, may as well replace the pump impeller and all seals at the same time if your washer is aging, save pulling out from under the counter again..