Under WI Stat. 709.02, "a seller of real estate is required
to potential buyers all known defects
within ten days after acceptance of an offer to purchase
the property....according to the plain language of WIS. STAT. § 709.03, a seller is not required
to disclose all possible hazards
associated with a characteristic of a property." Hoekstra v. Guardian Pipeline, LLC, 726 N.W.2d 648, 2006 WI App 245 (2006).
In plain english, if you know about a past defect, then you must disclose, regardless of how long ago the defect was known. However, you do not have to disclose any possible future defect.
You have apparently remedied the past defect, so you no longer need to disclose its existence. However, were the problem to suddenly become a present defect again, the buyer will undoubtedly claim that you failed to disclose a past defect. So, you have to choose between disclosing that which you are no required to disclose, as a means of avoiding the possibility of legal action, even though you may ultimately prevail -- or, not disclosing and accepting the risk of legal action, which may be resolved in your favor, but which could create substantial litigation costs in the process.
Please let me know if I can be of further assistance.