1. The Rev D is newer than the G.
2. The Rev D is the one found on the Mk6.
3. Apparently the G holds boost better. Speak to your tuner because personal preference does play a role too it seems
4. They're both available from VW
Now that is right
The "D" is a
plastic on plastic seal so wont hold boost as well as a totally sealed diaphragm (like the "G").
Both work fine, although i've tried both and have to say, the "G" feels a little more responsive at lower revs and makes a bit more of a "hiss" when I let off the throttle.
Nick @ R-Tech smoke tested a "D" and posted a picture showing it leaking, which sounds about right as plastic on plastic is never going to be an air tight seal, which is why I went back to the "G"
If a "D" does leak, it wont be as noticable as a rubber Diaphragm splitting as it will only be a small amount down the side of the piston, however it means your turbo will be working harder to sustain the boost your map is requesting.