I have a Moen tub & shower single knob system that is leaking at the
control knob. Water is leaking out around the control knob (not
dripping out of the spigot) when the shower is in use. The control
pulls out to adjust water pressure, and turns CW / CCW to contol water
temp. It has become very hard to push the control in and out to turn
the water on/off.

Does this sound like a bad cartridge or something else? The unit is at
least 15 years old and has never been serviced. It is now leaking out
the back of the control knob (behind the shower wall) as well as in
front.

Thanks,
Art