A flying session had to be put off when I realized that my wing dowel had come loose. When the time came to repair it, I discovered something interesting. If you pull your wing dowel out and look in the hole, you can see a sort of recess in the structure inside the wing, into which the dowel should key. The stock dowel, however, isn't long enough to reach the recess, meaning that it is only anchored by the glue that holds in the first hole it goes through.
I didn't have any dowel of the right size to replace it, so I found a square stick and whittled and sanded it into a new dowel. The new one is long enough to reach in, and as a consequence it is held firmly in two places. I drew a simple diagram to show what I mean, the dowel is shown in red.