Spent the weekend replacing my main shutoff and my plumber wanted no part of it

I went through something comparable last winter when my laundry tub faucet started dripping constantly. The brass connections right under the sink had become relly brittle and were weeping right where the supply lines meet the stop valve. I decided to ditch the whole section and replace the feed line with a new flexible braided hose. It wasn't like your main line job, but it was still frustrating becuase the original fittings were just so corroded. The tricky part wasn't the soldering like you mentioned, but ensuring the new compression fitting was seated correctly without cracking the old valve body. I used a specialized adjustable wrench and applied slow, even pressure rather than twisting hard. Once the seal was tight, the constant sound of dripping vanished. Those tiny little leaks always feel way worse than a huge overflow because they just seem to go unnoticed til the bill comes. It sounds like the next job you have under the kitchen sink is going to require the same kind of careful prep work. Old plumbing just holds onto decay in the most unexpected places. I hope you find a good solution for that fixture.

I had to replace a stop valve under the kitchen sink last spring. It was a horrible cast iron ball valve that had literally rusted in place for twenty years. The original post mentioned a bad gate valve but mine was a standard brass shutoff piece that had seized up inside the wall, which was a real pain. I tried using a pipe wrench, but it just rounded the fitting so I went for the bigger gear puller. The wall was made of 2x4 studs with very little give behind the line. It took a couple of tries to get enough leverage to break the pipe away without cracking the surrounding drywall. I ended up going with a bimetallic fitting from a local supplier because the pipe had allready started to eat through at the connection point. It was a bit of a pricey piece but you want something durable for that kind of stress. The whole thing fit into the space, and after I cut and soldered the new piece in, the drips stopped and the water flow felt much more consistent, which was the main goal anyway. It was definatly more of a tug-of-war than the original post described, but it’s done now.

For that kitchen shutoff, hit the stem with penetrating oil the night before and let it soak. I had one under the bathroom sink that hadn't budged in fifteen years, tried forcing it and snapped the stem clean off. Ended up cutting the supply tube and putting in a new quarter turn anyway, wich honestly was the plan all along. If yours does turn, work it back and forth gently a few times instead of one hard twist, then keep an eye on the packing nut after. Half the time they only start dripping once you actually use them again.

That pressure improvement doesn't surprise me one bit, since a gate valve that has been sitting in the same position for years collects scale on the gate and the seat until it basially becomes a restriction in its own right. I swapped a seized one on my irrigation tee a couple summers ago and the flow difference was instant once the new ball valve went in. One thing I learned the hard way on my install: solder with the valve fully open, because if the chamber is sealed the heat soaks into the seals and can ruin them before you even get the joint done. Also ream the inside edge of your cut pipe, or you get a whistle at high flow later on.