The absence of fastners had me a bit confused, too, until I posted the same question here a while back. The arm is pressed onto a splined shaft, so all you gotta do is wiggle it while pulling. I used visegrips (and a wrag to protect the chrome). I think I applied a little pressure with a screw driver too, but don't mess up your cowl grill!
I bought a tool for removing the wiper arms it's made by K-D part # 2039. It looks like a set of pliers with "U" shaped jaw. When you squeeze the handle together the jaws spread apart putting pressure on the under part of the wiper arm and on the cowl. The bottom jaw is rubber coated to keep from chipping the paint. The tool looks a little hokey but it works great. It did the trick when I removed the wiper arms some dozen times trying to get them both even without hitting the moulding around the windshield. I think Lisle makes a similar tool.
I believe there is a "spring loaded ring" on the bottom of the wiper assy. that "wedges" itself against the splined post and prevents the wiper from getting loose and coming off. The tool depresses the ring and allows the assy. to come off. Simply pulling on it tightens the ring and it is VERY hard to get off. Yours may be different.
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