If you're positive your wiper blade is bolted down firmly with that ferrule thing in place, then linkage is a decent bet.
When tightening, hold the arm well so you're not putting stress on stuff beneath.
I think it's just a matter of removing cowl and cabin air filter housing. I haven't been there, but I thought it was very accessible. Have a look beneath if you don't have any luck tightening down blades. I'd start by removing them, cleaning them up and trying again.
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