Tech/maintenance Octave G flat and weak.

[Mix O Lydian]

Yamaha 62 alto. When playing octave G it is coming out flat and weak. It seems to have started in the last two days. Only occurs on octave G.

I play the saxophone daily for at least two hours. This is a mechanical issue. I I know it's not me!

The octave mechanisms on both the body and the neck appear to be doing what they are supposed to do.
What could this be?

 

[Colin the Bear]

Leak at Bis or G#.

 

[Mix O Lydian]

Leak at Bis or G#.

Oooh!
Doesn't sound like something I can fix myself then!

 

[Targa]

Oooh!
Doesn't sound like something I can fix myself then!

It might be. If you stare at the mechanism for long enough you can see how the regulation works and a leak might be as simple as adjusting a screw or adding a bit of cork.
If you think you can see perhaps if a bit of cork being thicker would make the key tighter you can slip a piece of ciggy paper under it and see if it makes a difference.

 

[Mix O Lydian]

I just found this little bit of felt dangling from the G# mechanism. Explain why the fault occured quite quickly. Must have come unstuck. I suspect this is the culprit?