Water dripping from end of shower arm

First thought I had a leaky shower head, but it checked out fine. When I removed it, water still leaks from the end of the shower arm. Took off the cap and unscrewed our Moen tear drop knob to tighten the inside valve, but it's still dripping. What else can I check?

The culprit should be the cartridge. I suggest replacing it.

It should be this





Or this

leak

Showeer heads do not leak. The valve that turns the water on and off leaks. Tightening the cap on many new valves does not stop a leak, it just makes the valve harder to take apart when you decide to fix the real problem.

Cartridge replacement fixed it!

Thanks for all the advice! I got the Chateau Posi-temp Tub/Shower Replacement Cartridge (Moen part#1222) at Home Depot. The Home Depot guy said I didn't need the cartridge puller tool because a twisting tool (white piece) that already came inside with the cartridge would do the trick.
However, I read on many sites and on this forum that sometimes that thing doesn't work, so I bought the pulling tool anyway...just in case.

Got home and followed the instructions provided with the cartridge. So far, so good, until we got to actually pulling the freak'n thing out with the little white twisting tool they supplied. I'm not what you call a "petite man"...so I kept pulling on that sucker and it wouldn't budge. The wife thought I was going to yank the pipes out of the wall, so I went to the shiny pulling tool I bought and a few minutes later, out slides the cartridge.

Put everything back together, turn the water back on, crossed my pliers, feet, whatever...and asked the wife to turn the shower on/off for testing. To my relief, NO MORE LEAK!!! Many thanks for all the advice!