Does Dolnet Series 2 have problems with stuffy D2?

Having spent many hours trying to tune my Dolnet (using MusicMedics balanced venting method and also the Uppers, lowers and mids guides), I have nearly everything in tune, and with a good sound.

I am however having a problem with a very stuffy D2.

After searching on this forum, I have found a lot of useful information, and have used the info to set up the sax.

I have tested for leaks, by placing a latex glove over the bell, pressing the pads closed with the keys and sucking in. It takes about 30 seconds for the vacuum to be released, so I am reasonable certain that there are no bad leaks.Knowing that a vacuum test is not 100% as the vacuum will tend to hold the 'closed' pads closed, and under normal use the air pressure may open these, I have also ensured that these are closed by using wooden wedges.

The D2 is a vented key, and its tone is normally controlled by the key height of the lower C2.

I have almost got D2 to sing by completely removing the felt bumpers on the C2 keycup (so that the key hits the metal of the key-guard) , but even that is not enough.

If I press the C# key (to allow more venting, then the D2 does sing, bearing out the fact that the C2 is not set high enough.

Before I start altering the C2 key-guard to gain more height, does anyone have any more ideas I can try?

Of course I could just learn to add the C# fingering whenever I have to play D, but the ergonomics would make my pinky very tired.

All and any help will be gratefully received.