I think I would mention the make/model of the washer and the age, and then something like, "In good condition except that the plastic cowling on the opening has been shredded, leading to minor damage of delicate clothing." (If that's an accurate description.) Maybe someone will only want it for heavy-duty fabric, or maybe someone knows exactly how to fix that.
If you want, you could add something like, "This model is known for having mold problems, but I never experienced that with this machine." I don't think that's strictly necessary as I think it's incumbent upon the potential buyers to research models before purchasing; they could always ask you specifically about it, and you can honestly say it wasn't a problem for you.