If you know about it, you must disclose it.
Every home owner that puts their home on the market to sell must complete a "Seller Disclosure Statement". This is a 5 page form that tells any potential buyer everything that you as the homeowner know about the home in the time that you have lived there.
I know this can sound scary to a homeowner of a 1910 home that has had many issues through the time of ownership but for most owners I assure you this is nothing to fear. Buyers understand that things happen to homes, and furthermore, anything can be fixed.
When filling out the form be open and completely honest about every issue you have had. There are legal remedies for buyers that recieve false or misleading statements from the seller. Also, if a buyer has agreed to purchase your home, they will have an inspection that may expose anything that you haven't disclosed thus making them wary about your truthfullness. They may wonder what else you haven't disclosed and will possibly terminate the purchase.
So the rule is, if you have a question about whether or not to disclose any issue with the home, the answer is yes. Disclose it.