get some thick ABS cement, and a piece of ABS pipe. Use a horse shoe file and make a pile of shavings of the abs. Mix it in the ABS cement to make a pretty thick mixture. Then clean the ABS joint with alcohol and make sure it is completely dry. Then do a final clean with MEK, or Acetone.
spread the mixture of home made thick ABS cement on the joint, let it dry, repeat a couple of times to build it up. Wear disposable gloves when you do this and if needed spread the ABS cement with your finger.
You could use just straight ABS cement just takes longer to build up and fix the joint, Your solvent welding so in addition to sealing the leak, it is welding and strengthing the joint.