Goodnight, Seattle (1) - S11-E23
Revealing mistake: You have to be very quick to spot this, but when the cannon goes off Niles drops the ring, you can actually see it drop between Eddie and the camera and bounce away from Eddie. In other words, it certainly doesn't go anywhere near the pate.
Answer: It equals the record of James Arness of "Gunsmoke" for the actor who's played the same part on TV NOT in a soap opera. If you include soaps there are two main contenders - William Roache, who's been playing Ken Barlow in "Coronation Street" in the UK since 1960. Don Hastings has been playing Robert Hughes in US soap "As the World Turns" since 1960 as well.