I work a 40 year old apartment complex. Most of the plumbing fixtures are Moen products. In some cases I have been unable to remove the cartridge to resolve a leak in the faucet. I have a cartridge puller but in a couple of cases I have actually pulled the stem (center section) out of the cartridge and have had to replace the entire faucet. Is there a trick or technique to removing these "stuck" cartridges or am I missing something (and yes I am removing the retaining clip and attempting to twist the cartridge loose before pulling)?
It is really aggravating to have to remove and redo the ceranic tile and replace a tub/shower faucet that drips. Any suggestion are appreciated.

It happens to all of us with those old Moen cartridges, so don't feel like it's you. No real secrets to it, but it may help to get an easy-out kit. I found one made by Plumbest (I think... threw the package away months ago.) at Home Depot. There is a size in the kit that fits inside the cartridge casing and with some twisting and patience you may be able to work it loose. Be careful not to damage the valve body, of course, because the new cartridge will not insert properly if you do.