The part that's coming off is supposed to be held on by three screws, no glue. It looks like one or two of the screws are still in the lens. So the question is, why glue it? The person who glued it might have tried to fit a part from another lens like the 55/1.8, which isn't the same. They might have hacked up something else. That would be the only reason not to repair it.
If there isn't a part problem, you might be able to fix it yourself. See if you can unscrew the "name" ring, the beveled ring engraved with the lens name and serial number. It should unscrew using the filter threads, and you can get a better hold on it now than usual because of the filter ring falling off. You should be able to see if any other screws are still holding on the filter ring. It looks like your lens uses slotted screws so an eyeglass repair kit might have a screwdriver and even some replacement screws too.
Here's a photo of that lens with the filter ring removed. The little tabs each have a screw hole in them for one slotted screw.