Hello jakeru,
the 6-speed has 2 selector input shafts. The "big" one and the "little" one (green arrows). Cables go to the black rounded parts with the inner silver part on the photo.
As you can see, the weights on the big one are pretty massive (red arrow on top one).
Both selectors work together simultaneously. The big one has 3 rests / positions, not 6.
And the little one is part of the differential housing.
Inertia. Hm, i would say weight instead of inertia. Maybe a translation problem. Not shure if we mean the same thing.
Spring A: yes you're right when it comes to the gear stick. But i think the mechnism is different on the 6-speed. I couldn't find a picture that shows the 2nd hole as in the diagram.
And that won't solve the problem of duncan11, because that will affect all gears. That's why i mentioned the springs of the gear detents. But i think there must be another internal problem with a claw or something else.
But considering this post of duncan11:
http://986forum.com/forums/general-discussions/62915-gear-change.html maybe i would start with a change of spring A.
Regards, Markus