JimL recommended LPS 1 for brake cables. I ordered some. It arrived and I put it on the shelf until I could think of a use.
Sixteen months ago I installed a drain with a popup stopper. At first it worked great. Then it began to act as if badly corroded. It would resist being pushed down. Often the sink would drain slowly because it hadn't popped open quite all the way. Once I used a syringe to empty the sink because I couldn't pop the stopper open.
This would be my first task for LPS 1. I removed the stopper, dried it with a hair dryer, and cleaned what I could with a toothbrush. It wouldn't come apart further, so I gave it a quick spray. Almost immediately, the mechanism worked smoothly, and my hands felt gritty. Apparently, part of the problem was that grit had bonded to the metal surface. LPS 1 had gotten it off immediately.
I should have masked the seal. Some solvents make some plastics swell temporarily. The seal on the plug was wavy as if swollen. I shouldn't have put it in the drain because I had to remove the trap to push it back out from below. In a couple o hours the seal was back to normal.