How do I replace the piston and nut? For this model, do I need to disconnect the water lines (remove the DW) or can I do the replacement from the inside?
Do I need any special tools?

Is it better to try the over-night vinegar treament?

Please advise? Thanks!

GSD5910F00AA

Here are your parts, it has a parts layout which may help.
Replacement parts for GSD5910F00 models | AppliancePartsPros.com

Note this these units usually leave some water in the tub, a quarter inch or so. The pump seals will burn out if the pump is run while dry so if you bail out the sump to check it refill it with water before starting the unit.

How do I replace the piston and nut? For this model, do I need to disconnect the water lines (remove the DW) or can I do the replacement from the inside?
You can do it from inside with the water line still connected.
If you have a lot of water in the bottom of the tub bail it out.
Remove the slotted cover from the back of the tub.
The piston and nut should unscrew.
I would also remove the sump cover from the center of the tub and check it for debris or anything wrapped around the chopper. Be sure to note how the inner part is installed, reinstall it wrong and the chopper will eat it. Also be careful as often there is broken glass in the sump.

Do I need any special tools?
Not that I know of, a small socket set should do it.

Is it better to try the over-night vinegar treament?
Unless you see calcium deposits in other areas of the unit I do not think this will do much.

NCPDDAD17

Will this cause the unit not to drain.
It usually will not cause it to not drain at all but it will cause excess water to be left in the bottom of the tub. It makes the draining inefficient as part of the drain water comes back into the tub instead of being pumped out.

NCPDDAD17

so if it wasn't draining you think it may be this
Yes

and possibly a partially clogged line?
Yes

Also do you know if an appliance repair shop would carry this part, I live on Long Island in New York.
Sorry I do not know but it is a part that fails on a regular basis so odds are good that it will be available.
I do know that it is available from ApplincePartsPros and I have seen many people compliment them on their fast delivery.
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