So I fixed my first flat in the garage with a plug-n-go kit. I am worried I may have reamed out the puncture hole a bit too much, though. I got it plugged, but it now seems to have a slow leak, and is losing 2-3 psi a day.
Quality string plug kits actually vulcanize from the heat of running forming a permanent bond.
This is what crossed my mind as I read your post. Did you run the tire up to heat after plugging it?
Another thing to keep in mind, and I'm aware of the $$ aspect here but, if the tire is original the rubber is pushing five years old no matter what the thread looks like. Just something to consider.