Ron Palillo—the actor who played Horshack on “Welcome Back, Kotter”—died this morning at his home near Palm Beach, FL from an apparent heart attack … this according to someone close to the actor. We’re told Palillo was found by his partner of many years, Joseph Gramm, around 4:00 AM. Gramm called an ambulance and Palillo was rushed to the hospital, where he was pronounced dead. We’re told the heart attack was very unexpected. Palillo was 63. …