I have a similar experience. I bought my MOXF8 brand new in June of 2017.

By Christmas C4 had started rattling around, being noisy and feeling a little bit softer than the other keys. I went back to the shop at the beginning of this year (the big Yamaha Music shop in London) and was told I had to bring it in so they could send it off for repair, which from where I live is about a 30 pound cab ride. They also weren't entirely comfortable lending me a flight bag to have something to transport it in.

Since life was a bit chaotic at the time, I decided to leave it for a few weeks as the guarantee is for 2 years anyway and so there's no great rush - it's still playable, just annoying as fast runs that pass through that note don't sound even, even though when I play them on my piano they most definitely are being played evenly!

Since then the adjoining C#, D, and B keys have started going a bit wobbly too so I'm wondering if I should wait even longer before sending it off for repair in case something else gives.

I give it what I think is reasonably normal use for an amateur musician - maybe 1-2 hours play a day, more at weekends, so am surprised that the keyboard has started playing up so soon.

I wonder if I am alone? I will get it fixed, I just don't want to send it off for repair for 2-3 weeks for it to come back and then another key goes almost immediately!

David.