Well here it is from MFS in an email,
Steve,
With the last few shipments we received from them the boxes have been marked 3.8 which caused some confusion when some customers received them. We contacted Innokin to inquire about the size difference and apparently they redesigned the chimney and coil housing so it’s more efficient but does hold a little less liquid. I have included the picture of the differences in the two tanks. If you have any more questions or need anything else, please let us know.
Thanks,
David Hammer
So it seems now there is three versions of the G tank, and by the way each of my rba builds are leaking and are needing new cotton. They aren't tasting bad, just letting juice seep and going into the 510 connection.
On one I took the airflow cap off and installed and used it that way, so I could watch it closely for leaking. It worked fine but you have to be careful not to lift on the tank as it will come right off. It hardly leaked at all for a day using it like that, though it looked like pretty robotic...lol