Wiper post knock, loose

OK, I've searched Naxja and other Jeep forums without any luck. There are plenty of posts about replacing bushings in arm mechanism, but that's not my problem...those have already been replace and are tight.

My problem is with posts on which the wiper arms mount. They have some up/down play in them due to worn metal/rubber washer. This causes them to make a knocking noise at each end of their travel. I can probably find a substitute washer, but I cannot figure out how to disassemble the post. The bottom of the post is welded to the actuator arm mechanism. The top of the post, where the wiper arm mounts, has a slotted fastener that is shot-peened in 3 places. The slot is not deep enough for a slotted screw driver to get any bite. So it appears there is no way to get this loose without drilling it...and if I do that, I don't know any place to get a new fastener. It looks like a specialized fastener is extremely flat head.

Anyone have a solution for fixing this?

Get a newer/better shape wiper transmission from your local pick and pull.

I would second the replacement, but if you cannot replace, or if you just want to try something first, I'd try drilling out the fasteners. Maybe even try twisting off the top and shearing them if you can't find what to drill. Then for replacement drill a little hole through that's a tight fit for something like welding rod or a small finishing nail to use as a new pin.

If you can get it apart, I'd look for a curly washer.