I'll Fix It - S4-E2
Deliberate mistake: After Roy and Johnny rescue the man trapped under his house, when the ambulance reaches Rampart, in the shot from inside the ambulance when Roy follows the stretcher out, he stops at the receiving doors and waits for John, who just arrived in the squad, and in this semi-closeup, it's odd and very apparent that it's not actually Randolph Mantooth, it's his double meeting Roy at the door.
Answer: I believe you are speaking of the old man, Mr. Wilson. He's played by J. Pat O'Malley.
Bishop73
Correct, it was J. Pat O'Malley...he also played the grandfather with his grandson when their rocket exploded, and also played "Old Bill" in the episode with Ann Prentiss, where Gage saves the little girl from the burning tree house, and her mother falls in love with him.