Tom Selleck, 78, is reportedly dealing with a private health issue, battling arthritis-related pain. Despite using a stunt double for routine scenes on “Blue Bloods,” Selleck continues to work and has sought medical help. Insiders suggest his commute from his ranch to NYC for filming takes a toll, and sources say he’d rather spend time with his family. While his reps claim he’s “fit and vigorous,” insiders acknowledge Selleck’s physical limitations, praising him as a dedicated professional who doesn’t complain.