If you're selling, it may cost you less to just disclose the problem and let the new owners fix it. Basement leaks are pretty common, especially in older homes. Buyers know this (usually) and will want to take money off of the selling price - but it may only be something like $500 - $1000 (I don't know, I'm just making those numbers up.) Don't spend more than you'll get back in the sale.
Ask your real estate agent how much perceived value you're losing because of this problem. A slight water problem in the basement is not such a big deal to a lot of buyers (as opposed to a leak in the roof or an old-looking kitchen.)