Moen shower head drips. Single lever shower only. Installed by home builder about 2001. How do I fix the drip/leak

Hopefully you had the correct type of cartridge for your faucet.
I would suggest watching this YouTube video to make sure the cartridge was inserted and fixed correctly. The travel of the cartridge may not be aligned correctly. Hard to think of anything else that could still cause the drip.
How to repair replace leaky moen cartridge on single lever tub shower...

You need a replacement cartridge or faucet washer on that shower control

if there is not a shut off for the shower you may be out of luck.

remove it and carefully inspect it, you might have scuff'd up the rubber's on the cartridge when you inserted new one.clean out,look in hous'ing for any foriegn mat.etc .you may need another new cart.

Make sure the drip is continuous because the shower head will drip for a few minutes until it empties out. Replace the cartridge or washer kit if it keeps dripping.

the problem is in the shower fitting the part with the handle ,depends on who made it but you replace washers or a cartridge some times easy some times not

It sounds most likely to be a bad cartridge.

Hope this helps

Check around the the front of shower and make sure there is no place that water can seep thru such as old calk and or loose tile and around fixture molding

If it is dripping from the connection where it goes to the water spout you can unscrew the connection and wrap teflon tape or Pipe Joint Compound on the Threads. Now you can Thread the Shower Head Back on, with No Leak. IF..... It is leaking from the Shower Head Itself There May Be a Problem with the diverter handle/lever. If it has a Pull Type Lever, sometimes you can screw the Lever up or down for the proper water restriction to the Shower Head. However if the Hot and Cold Handle/Lever is OFF, There should not be any Water coming out from anywhere! If water is coming out off the Tub Spout, with the Shower Off, then you will have to replace some washers or Cartridges in the faucet(s) to stop the dripping. You can do this easily....Just Ask) Remember though, that some shower Heads may Drip for a Few Minutes After they are Turned off. There is still water in the Supply neck and needs to escape, either though the tub Spout or Shower Head.......Hope this Solution Helps you with your Drips.....Joe

coming from the uk it sounds that when you mention it leaks at night its a possibility thats when the water pressure increases & the valve starts to drip?

i know its not a solution but it may help you understand why its dripping at night.

Also the seals might be damaged in which case thats why its dripping check them for damage. make sure when you put the new cartridge in that you put some silicone grease around the seals as this helps the insertion & helps protect the seals from damage.

Kindly

Richie