I need to splice into an ABS stack that is 40 or more years old. I'll be using PVC and generally know how to do it, but I've read that ABS gets brittle as it ages. Is there any special advice on how to cut it other than "be careful"?

If I were doing this I would take a Saws-All,( reciprocating saw) with a fine tooth blade and make my cut without putting too much pressure on the saw blade. Take your time and go slow. Good luck, Tom