[AntiImperialis4]

Definitely don't. Nothing good will come to you from it.

You abandoned it for a reason and only people who'll benefit from it are other people. That would be fine if it was not at your expense. Someone may look at the source code and contact your support or even take you to court because one of your programmers ignored license of a third party library. You could get it audited and re-write parts of it... even so, there is a non-zero risk that someone will come after you.

If you're OK with that, do what you want. Otherwise, by default, don't opensource your abandonware.

[nerdponx]

This is why many open source licenses come with explicit warranty disclaimers.

[AntiImperialis4]

That doesn't protect you against violating someone else's license. If you never make it opensource, nobody has to know.

[nerdponx]

Good point, although what would cause a situation like this? Releasing source code with a modified version of a GPL-licensed library, but with an incompatible license? Wouldn't that be a problem when you're distributing software anyway, regardless of whether it's open-source or not?