Check out our friends at Amazon
Valterra T84 3" Hub x 3" Hub x 3" Bay with Cap Double Ell Rotating Valve Assembly
https://www.amazon.com/dp/B00594B73G...I20DFKYMRK7I0L
Use Fernco rubber hub to pipe or hub to hub sleeve connectors to connect the new assy. no need for a plumber.
just curious, why not just replace the valves or is that a leak at the elbow?
If you have a leak in the area of the elbow shown in your photo, as the dirty area at the joint, then this can be easily fixed with a Fernco hub to hub rubber sleeve connector...very easy fix and the rubber joint will fix the vibration issue that possibly caused the leak that appears in the photo.
Pertinent posts trying to help ...not a campfire builder