Removing Valve Stem

[RonG]

I tried to remove and replace this bathroom valve stem and found the 5/8th socket just turned turned due to rounded corners on the stem. I had a plumber come out and he couldn't remove it either and recommended removing the drywall behind the faucet to remove the valve stem.

Does anyone have any recommendations how to get this valve stem out?

Thanks

 

[Geofd]

What brand is the faucet, show
the trim it's will be easier to identify

 

[Jeff Handy]

Did you use a six sided socket?

A 12 sided one is more likely to slip on rounded nuts.

 

[havasu]

Spray penetrating oil and let it sit overnight before any other steps. Also, WD-40 is NOT penetrating oil!

 

[johnjh2o]

Try a set of these.
https://www.homedepot.com/p/Husky-Shower-Valve-Socket-Set-16PL0132/304217601