Older Moen tub/shower valve leak

I have had a leak from an 23 yr. old Moen (push-pull) tub spout... and am finally attempting to repair it. I disassembled the unit and replaced the cartridge. I believe I have the problem solved but now there is a leak coming from a screw on the brass housing itself, which was not noticeable before. I may have disturbed an o-ring when I tried steadying the unit with my hand, dismantling it.. rubber is slightly protruding on one side from around the screw. I am afraid to open it up, because I don't know if I will damage the unit beyond repair..
of the two screws on the housing itself, it is the larger one on the right which is leaking...it is about an inch in diameter... the smaller one on the left seems to be fine.... I have tried to find some reference to a teardown on the internet, but am confused as to which one it is... it is old and probably is a discontinued model...
Thank you to anyone who can help.
Gayle

Are you referring to a hot or cold side stop valve, as shown in this diagram> http://www.plumbingpartsdepot.com/moenlegendtub.pdf

Hi Jimbo..
Thank you... I am so happy to hear from you...
I am attatching a photo..???
or linking
https://terrylove.com/forums/attachment.php?attachmentid=3095&stc=1&d=1193359874
It is the very large one on the right of the stem...
you might even be able to see a droplet...
Talk soon
e-mail is signstudio@swva.net
Thanks
Gayle

You have a Moentrol, like this>http://www.plumbingpartsdepot.com/moentrol.pdf

The part that is dripping is the balancing spool. Apparently one of the o-rings got pinched going in. Get a new spool, or a supply house might have an o-ring kit for it. While it is out, use some crocus cloth , or 400 grit wet/dry to make sure the outer entry of the body is clean and smooth. Then use some plumbers grease or silicone grease on the o-rings, and try to reassemble.

Jimbo
Great lead!
I think I can take it from here and all should be okay
Thanks again
Gayle