Leaking ABS joint in drain pipe.

My wife noticed the ceiling bulging in our first floor family room. I cut out the drywall and found a leaking ABS joint in the drain pipe for the 2nd floor bathroom.

Should I cut it out and replace?

Or just use a heat gun to warm up the joint and slather ABS joint compound on it, in an attempt to get the compound to draw into the gap and reweld the bond?

Thanks!
Note, image is rotated -90degrees.

 

Just cut it out and replace. For $15 worth of fittings it's not worth trying a hack. Make sure you use ABS fittings and ABS solvent cement.

 

Yup, what Paul said. Use no-hub couplings (rubber couplings with the metal shield) to make any connections that you can't cement.

 

Thanks. I ended up being able to cement all the coupler joints. Letting it cure now. Also need to dry out the framing that got wet and moldy. Not too bad, but I will probably wait a few days before finishing the drywall repair.
Note image still rotated -90 degrees.

 

Clean the wood with straight bleach, it already looks pretty good.
Keep a fan on it longer if you can, it won't hurt.
The cement can be used immediately, no cure time.
Good Job!

 

Thanks again.
The hardest part was measuring the exact lengths to cut out and the lengths of the replacement 2" straight ABS pipe to join the existing pipe to the new couplers and elbow. Also because the old pipe had no give (i.e. would not move back in the direction they were coming from or going to) I had to think long and hard about the order of assembly. I was stumped and went to the old orange depot to get a no hub coupler but on the way home I figured it out:

1) Each side of the coupler takes in about .75 inches so that takes up about 1.5 inches total. Then the elbow also take in about .75 inches so it's just a matter of cutting a small section of straight 2" diameter pipe to about 2 inches (this was as small as I could make it to make up the 1.5 inches for each .75 inch coupler insertion and a little more to cover the section that I cut out). I had to make a couple of extra cuts on the exiting pipe to give me enough room to work. I used a wire saw like this:
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2) Start by cementing the first coupler on the upstream end of the old horizontal pipe in place and work down flow.

3) Then on your workbench or the floor (i.e. not inline on the drain system itself just yet), assemble the 2" straight horizontal section, elbow, and another straight vertical section to extend through the wood framing down to the final joint.

4) Extend the vertical downspout section through the frame and attach the elbow assembly and straight horizontal 2" extension to the coupler you started with in step 2.

5) I was able to push the horizontal pipe, coupler, elbow and short 4" vertical section up enough to attach a coupler on the end of my short 4" section of straight down pipe.

6) Then the final coupler to the rest of the old vertical pipe.

It's a little hard to control the cement inside the couplers. Some cement spilled over from one end to the other. I worked fast enough that this wasn't a problem. It's amazing how fast the materials weld together so tightly. Pro tip: wear nitrile gloves and have some paper towels handy to wipe up excess cement that spooges out of the joints when you push them together.