Usually when I'm watching stuff, there's a rule I go by: "Stock footage: take a drink." For this particular episode (S07E21 Hit Gun For Sale), I would be toast prior to the halfway mark, never mind the rest of the episode. It is replete with stock footage and it would seem to be a top contender for the episode that uses the most stock footage.
Can you think of any other episodes where there is a lot of stock footage in use? Was there any other episode that might have used more? Which episode did use the most stock footage?
And by the way, the use here was appropriate in my book as things fit where needed. It makes sense too, if you don't have to re-shoot something, your budget doesn't get eaten alive by principal photography.
Just my two cents.