I understand your problem completely now, although I haven't ever seen or heard about it. In the first picture you will see the cover and arm. The blue arrow points to some type of cover for the pin (glob of something), and the red line is where the pin rides, keeping the arm in place. There are a number of ways to fix this problem. Here are two....First being to take a chisel and knock off that cover "glob". If there is in fact a hole there go to a auto parts/Home Depot/Lowe's and buy a split pin. Measure how long you need it, cut to fit and use a drill to drill out the hole larger or drill a hole and tap the split pin in. Do this with the arm in. It can be done with the arm out but you might tap too far. Make sure arm moves freely. The other thing you can do is drill, tap and insert a set screw. There is plenty of room under the cover so a little extra length won't hurt.
As stated above a nail or drill bit will do but with a split pin no gluing is needed... Personally I'd go the split pin route.