cut the offending section off,
use two of these types but for the right diameter of pipe:
http://a.co/92LGD1d
(you can even get ones with reducer to go from old to new if theyre different sizes)
and then cut a section of new pipe, and make a new elbow ... (you could even use plastic like pex or ABS) to fit the gap, and use those rubber clamps to hold it in place
I'd probably just glue one together with ABS and glue...
probably last years