I have also had to run a tap thru them to clean up the threads. I seat blind nuts with epoxy, and get a bead of epoxy around the barbed flange. I never had one come loose. For oil soaking protection, I coat the hole with epoxy, using a pipe cleaner to get a thin layer of epoxy in there.
Another problem that sometimes shows up with blind nuts--the threaded barrel section is not always perpendicular to the barbed flange. If you install it so that the flange is in contact with the wood, all the way around, you might find that the screw has to go in a bit slanted to get it in at all. So, before you get everything in place, run a long screw thru the blind nut from the back side and see if it starts binding up before it gets all the way thru the hole.