washing machine leak?

I noticed that there are water marks or stains on the vinyl floor underneath my Whirpool washer, near the legs in the back. Water has apparently leaked in the past but doesn't seem to be leaking now. Any suggestions on a possible explanation? I am in the process of selling my house and want/need to fix the problem if there is one. Is it possible that the washer has leaked under some unusually situation in the past but generally doesn't leak?
thanks for any help or suggestions.