Regarding Arthur Marino's request for information on the 1/16th elbow
on the bellows:  Arthur, I too have a 1/2 Duo-Art (American made Steck).
The elbow on the bellows (on my instrument) is the vacuum feed to the
tracking pneumatic.  It goes from the bellows up to the connector block
on the stack and from there to the middle connection on the tracking
pneumatic (on mine)

My piano uses the tracking ears system so may be different to yours?  
I wonder how your tracking system is currently fed vacuum?

I hope that helps.

Andy Hood (Northeast Scotland)