Hi--
I replaced the moen cartridge, single lever, kitchen. The first time it started leaking after a few days. I took it out, flushed out the water line, reinstalled and now leaks as soon as I turn the water on. I looked inside the tube (?) and saw some corrosion. Could that be the problem? Should I try replacing the o-rings?
Thanks,
Mike

Did you lube the "O" rings with Silicon Jel when you installed the cartridge?
Check the "P" rings. Are any rolled out of position?
saw some corrosion clean off any corrosion that's in the valve body and try again. Good luck. Tom

You may also have made or just got a small nick in an O ring. If Tom's suggestion of silcone jel doesn't fix it just call Moen for free replacement and start fresh, they give you some jel with the cartridge.

I was having the same issue. After removing it for the third time to return it. I was staring at it for while and realized that the end where the handle attaches to (brass end) was pushed in just a little bit leaving a gap in the holes that are covered by the Rubbers on the sides. I just pushed the other end back in (pushed the cartridge back in place) and it was good to go. Make sure u use the plastic installation tool that is provided so u don't inadvertently push it out of place by pushing in on the brass end. No more drip!