[...snip...]

The second idea is that I came across a product that is basicall small
metal strips that have serrated teeth. These are used to wrap around
the dowel or mortise and reinsert back into the joint. Made by
"Woodmate's" and called "Mr Grip Furniture repair kit"


I've used those. They do help loose joints grip. I don't think they
would work well over the long haul in a chair, however.