I've never used Slime or equivalent. Always patched. Many of my flats are form radial tire wire and (unless there's a secret I don't know yet) very hard to find with the tire on the rim. I do a quick inspect of the tire first, If I don't find the cause, I pull the tire and tube off, blow up the tube and find the hole, patch, then use the patch to locate the issue in the tire to look at the cause and damage to the tire. I have had second flats many times when I took shortcuts.

Basically what GuessWhoCycling wrote except almost 52 years, Actually close to GuessWhoCycling when you knock the sewup years out.

Ben