The easiest way in my opinion would be to locate a new identical valve, and swap the movable parts - unless something is wrong with the body of the valve. The plastic piece you mention is a sleeve used for Pex connections, but is mostly used by plumbers and is quite permanent. You can always cut the plastic tubing below it, but then you have other problems to solve... If that connection doesn't leak, I'd leave it alone, and swap the inside of the valve with new parts.

Thanks. That might be my best bet, especially since I don’t have a tool to crimp a Pex connection. I’ll see if I can swap the movable parts.

If that’s PEX supply line, you can cut the line directly below the plastic cap and crimp on a new PEX fitting. You’ll lose a couple inches of length so you may need a longer line to the fixture.

PEX is easy to deal with. I did an extensive plumbing redo in my master bath, all in PEX, and it’s fairly dummy-proof as long as you use the right tools and a go / no-go gauge.

Good luck!

https://youtu.be/gQ4Fkm2XTcU

This is how that plastic joint works. It's not reversible and not really something a homeowner will have the tools for.

Replacing the guts of the valve is likely your best bet.

You could also cut the plastic pipe and press on a sharkbite valve. That might be the easiest way to go.

Thanks. This will be my second option if I can’t just swap out movable parts in the valve. I believe it is a Pex line but is there anyway to know for sure? I’d just have to go buy a few tools if so since I don’t have any for working with Pex. Still cheaper than a plumber though.

Does Sharkbite press directly onto Pex, or would I need to buy anything else?

You can cut the valve off the PEX line. At various big box stores you can get sharkbite or other push to connect valves that will go right onto PEX so you don't have to use any PEX crimping tools. the push to connect are removable so you can replace it if that one breaks someday. Since it is under the sink and exposed, you will be able to see if there are any problems with the fitting. Some people do not like to enclose push to connect fittings inside walls.

I personally dislike PEX and push to connect. I would really prefer copper lines and good olde solder and threaded connections. But progress happens.

Yeah, I don’t know how you’d know definitively if it’s PEX. The stuff I buy locally ((Home Depot, Texas) is not translucent like what you’re showing but a quick Google search shows that it comes that way. I don’t know of any other kind of plastic used for supply lines (but I’m not a plumber).

Also I saw a reference to PEX-A and PEX-B….. life is never simple!

Sharkbite works with pex, copper, and cpvc.

That's Uponor/WIRSBO PEX-A, and you'll need a replacement sleeve and the expansion tool to install one. Amazon will sell you a hand expander set for a cool Benjamin.

Make sure that you shut off the main water valve.

I did this and it worked perfectly. Thank you!

Glad I could help!

This. Sometimes you can find a manufacturer or model on the valve by using your smartphone camera. Try several angles. Take those pictures with you to the stores.

Pex is relatively new so you have a good chance to find that valve still being sold.

Clean the valve seat (in the valve body) gently when you are reassembling. A small amount of faucet grease on the seal is a good idea but not required.

BTW: to avoid breaking a valve, when you start to turn, if it resists; turn just a little CCW, then back CW to tight, then back CCW a little more... Back and forth can break the corrosion up without breaking the stem. It usually works.

If you cut the pex line, you should be able to throw on one of these: https://www.supplyhouse.com/Bluefin-PAMA050-1-2-PEX-AL-PEX-Compression-x-1-2-Male-Threaded-Adapter

And then add this valve on it: https://www.supplyhouse.com/Bluefin-SSQ050F-038CS-1-2-FIP-x-3-8-OD-Comp-1-4-Turn-Straight-Stop-Valve-Lead-Free-Chrome

And you're done. Probably assemble the valve and the pex compression with tape/dope before putting it on the supply line.

They make a poly fitting but they are limited in functionality. You could use a poly coupler, transition to pex then use a sharkbite

Definitely better to replace that valve with a ball valve, along with the other one.

As others have mentioned that is pex, and is very easy to work with.you could install a sharkbite shutoff as long as the flexhose to the faucet will reach the new, slightly lower threads

Once you get this repaired, it's good practice to open and close these valves on your sinks and toilets 2 or 3 times a year. Keeps them operating properly so they work when you need them to.

Recommend one with a metal stem.