Here are the capsule photos you requested. I added two photos from the circuit board as well.
From the images posted the capsule doesn't look too bad, honestly, i.e. pretty normal for an older/used mic I'd say, but I'm not an expert. (Of course you can't tell for sure from a visual inspection whether there would be issues.)
In terms of DIY cleaning, I read enough about the process to be scared to attempt it myself with a mic I cared about. I started to try but ended up sending it away. That video seems way more aggressive than I would ever dare be, but I'm no expert and will let others more knowledgeable weigh in. And of course this could be a good practice mic for your technique, so there's that. But I wouldn't bother heading down that road until/unless an expert here agrees that it's a potential explanation for your symptoms.
Btw: Yesterday I registered the microphone with Rode. They promptly issued an extended warranty for the product until 2034. Maybe I'll send it in and ask for a cost estimate for a repair.
Heck yeah -- especially if it's under warranty that would definitely be the way to go. :-)
-c
