Straight from the horse's mouth - Mr. Maharis says:
As for why he left “Route 66,” Maharis emphatically said it wasn’t because of demands for more money, or that he was trying to break his contract so he could get into movies. It was, he said, because of hepatitis problems starting in 1962.
Maharis was hospitalized for a month and missed several episodes because of the disease. He returned to the set and its 12- to 15-hour days. A few weeks after a grueling scene where he rescued a woman from a near-freezing creek, Maharis suffered a relapse.
“The doctor said, ‘If you don’t get out now, you’re either going to be dead, or you’re going to have permanent liver damage,’” Maharis recalled.
“I wasn’t interested in leaving the show. I enjoyed it; I was having a good time. It probably could have gone two or three more years, and I think they even had plans of taking the show to Europe. That’s what they talked about, anyway, and I would have looked forward to that.
“I was trying to recuperate, and there was all the crap going on about how I wanted more money. It was all garbage. Some people even tried to make it like I never had hepatitis at all. But it’s all in the doctor’s reports.
“I was just ill. It took me 2 1/2, three years to recuperate before I started working again. What should have happened, I guess, was that I should have worked only a couple of hours a day.”