We recently purchased a Dimension 3D ABS Plus printer.  The pieces were coming out great size wise but they leaked like seives.  Dimension wanted $80 for a handball can size container of sealer.
Someone told us to try MEK, methyl ethyl keytone.  IT WORKS GREAT!
In general brush it on and it disolves a small amount of the ABS and it will skin over when it dries.  Add more coats for a better seal.  You can also glue pieces together if you use enough of it and moderate pressure.

Hope this helps someone.