The two credits here for John Gabriel appearing in Danger Man (The Mercenaries and To Our Best Friend) are in error. The John Gabriel in To Our Best Friend (appearing only in the teaser) is actually John Gabriel (III). In fact, the entry for that episode shows BOTH John Gabriel's credited as Rutledge, apparently because they weren't sure.

Not totally sure about The Mercenaries, but a quick scan through the episode doesn't show anyone looking like the original Professor.