Grampa vs. Sexual Inadequacy

S6 E10: Marge and Homer's sex life hits a rough patch, but Grampa perks things up with a homemade revitalizing tonic. He and Homer go on the road to sell their elixir, and Grampa reveals that Homer's conception was not planned. Homer vows to be a better father to his own children, then realizes that Grampa did care about him after all.