This is a molded tub/shower unit. I have opened a hole under
The unit an can see some wet places on the drainage pipe. Do I have to break this pluming apart an try to tighten the joints.

The drain for both the tub and the shower are one in the same. If you can get to the joints easily, just tighten them. It's not too common that these loosen up but it can happen.

Hi Steve

The tub/shower has an overflow assembly behind the tub (see picture below). Check for an access panel or you may need to cut an access panel at the wall behind the tub drain and check this assembly for leaks. Here, fill the tub to over the top of the overflow with water and check the entire mechanism for leaks. Once you find the leak you can determine if you can make a repair or if you are better off replacing the entire overflow assembly.

If after opening up the wall and inspecting the overflow assembly for leaks you find none at the overflow assembly then you'll want to check the hole in the tub/shower unit that allows a pipe to go through for the tub spout... may be uncaulked and need to be caulked to stop a leaker here.

Finally, don't forget to switch between tub and shower so that you are able to check the tub and the shower connections behind the wall... never do know where a leak will pop up!

Back to you...

Mark