Hi, i looked around this forum, and found much useful information regarding my problem, but nonetheless still wonder about a few things.

I live in san diego, where I've read the water is pretty hard. The faucet on the tub gradually started malfunctioning, and finally got to the point where turning it would not turn on the water at all. I looked online, determined I probably had a moen posi temp cartridge, and after watching a few videos about replacing the cartridge, I proceeded. That cartridge has been in there at least 12 years, probably closer to 15.

I bought the new 1222 cartridge at home depot, and a puller tool as well just in case. When trying to pull out the old cartridge by the shaft with pliers it would not budge at all, nor did that white plastic thing help to jar it loose. I used the puller, which broke it free, and pulled it out a little ways, but after reaching the limit of how far the puller could pull it (even after deepening the slots on side with dremel tool to allow it to pull further), the cartridge was still stuck, and not very far out of the valve. I had to grab the plastic part of the cartridge with channel locks, and rotate it back and forth through about 30 degrees while pulling as hard as possible. After about 5 minutes of this i got it out, and of course it was not in very good shape. For the record there is a part number on it which is 109272.

I checked the inside of the valve for debris and to be sure it was pretty smooth. i picked out a few pieces of rubber and plastic from the old cartridge, and rinsed the inside of the valve a few times with water. The insides felt pretty smooth to me, but of course I'm not a plumber, so don't really know how smooth it should be. No damage apparent to me.

I installed the new one (did not use any grease since i missed that part in the instructions). The new cartridge slid into the valve pretty easily with no problems, but after getting it all back together, to my dismay, the faucet now leaked at the rate of a slow drip when turned off. The leak lasts indefinitely...all night, next day...etc.

I took off the white spacer things with the gear like teeth and tried simply moving the shaft with pliers to see if perhaps something was out of line when the entire thing was reassembled, but even with none of that stuff on there, there was no spot in the rotation of the shaft that would result in no leaking. The best position resulted in the leak described.

I pulled it out to check it. It came out easily by pulling on shaft with pliers. It looked fine, and I figured that perhaps if I put in back in with some grease it might fix the problem. I had some bicycle hub grease, so put a dab of that on the o rings and proceeded to put it back in. this time I could not get it to go all the way in. I pushed on the shaft hard with pliers and the shaft all of a sudden slid towards the cartridge about 5/8ths of an inch....not all the way, but this was unexpected and made me wonder if that's bad news. The shaft now can be pulled in and out of the cartridge easily. Since I no longer dared push on the shaft to get the cartridge into place, I pushed on the plastic front plate. After pushing very hard for a minute or two, i got it in, but it leaks even worse than it did after the first time i put it in.

So from everything i've read on this forum it seems to me I have one of three problems;
1. the new cartridge was defective or I damaged it when putting it in the first time. Since it slid in easily the first time I don't see how I could have damaged it in doing so.
2. the new cartridge is not the correct one, although the new one looks almost exactly like the old one. (for the record the new one has o rings in the front and back of the cartridge.
3. i could have damaged the interior of the valve although to me (the untrained eye) it seems fine.

I'm looking for some advice on how to proceed. At this point I'm planning on going back to home depot, getting another cartridge, and trying it again, this time using some faucet grease, but somehow I don't have high hopes. I wonder how smooth the interior of the valve has to be? I feel no sharp ridges or edges.

Thanks in advance for any help you experts can provide.