I'm a Carpenter and I wouldn't even think of messing with an epoxy. You'll end up with big mess all over the fender that can't be cleaned up, or wiped off with a wet rag. After the crack, spit and break are all clean use some type of clamp to see if you can close the damaged areas to where all the cracks are closed and tight. If everything goes back with no loose splinters keeping the split from easily being closed, then you're ready to drown the splits with a good wood glue. I prefer the old Elmers Carpenters glue, it's still better than most all of the new crap on the shelf today. After completely covering all the splits with glue wiping it in to make sure of no voids, a very moderate clamping pressure is all that should be needed. Do not use excessive clamping pressure! Once it's clamped, wipe off the excess glue with a wet rag or sponge, and at that time you should be able to inspect the repair for any misalignment or other issues that might need attention. Dap Plastic Wood filler is made with coarse sawdust and a solvent based glue. It should be plenty hard and dense enough to fill the recessed area from the old rivet head and support the head of the new rivet.
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