I was too young in 1955-58 to remember when originally aired, but like a lot of others, loved this show in re-runs in the 60's. (I haven't seen it since)
I just received season 1 from Deepdiscount. This series has been digitally restored, is is phenomenally beautiful! The scenery and colors(especially the Sgt's bright red uniform), are just wonderful to see. I've watched about 8 episodes so far, and the stories are well written.
The only thing I've seen so far that I remember, is at the end of every episode,
Sgt. Preston says "Well King, this case is closed" to his dog Yukon King.
I wish it had gone more than 3 seasons, this is a good show.