MUST disclose. Not should. It's the law.
"68 Pa.C.S.A. Â§ 7303. Disclosure of material defects
Text of section effective one year from December 20, 2000
Any seller who intends to transfer any interest in real property shall disclose to the buyer any material defects with the property known to the seller by completing all applicable items in a property disclosure statement which satisfies the requirements of section 7304 (relating to disclosure form). A signed and dated copy of the property disclosure statement shall be delivered to the buyer in accordance with section 7305 (relating to delivery of disclosure form) prior to the signing of an agreement of transfer by the seller and buyer with respect to the property."