There's a general misconception out there that the VG used by vendors isn't already diluted. There may be some that add pure VG to their mix but I doubt it.
VG properly diluted for vaping at an 80:20 VG to H2O blend is about the same thickness of PG. People see pure VG and it is quite thick but
almost no one uses it in that form for blending. A "100%" VG ejuice doesn't exist. It is part nicotine, part H2O for the blend and part flavoring and flavoring base which is usually not VG (although it can be
some VG, again, usually diluted with H2O for people alergic to PG), so that an ejuice made even with a nic base in VG and a VG blend is still only about 65-70% VG and done properly it is not thick at all.
The ejuice I've used in eGo-t's and eGo-c's has been DIY using Decadent Vapours AG (Aqueous Glycerin - VG with distilled water) with a VG nic based Platinum Ice and DV's flavoring some of which is a PG base but also some flavors are better set in a combination of PG, VG, H2O or PGA depending on what brings out the flavor better. I have had very few leaking problems with the t and none with the c except for one bad atty holder. I've seen more 'leaking reports' from people using higher PG ratios vs the "no PG" blend that I use. It isn't "100% VG" because that only exists with pure VG and no one should be vaping that
And there are some PG ejuices out there that are thinner that others. When you apply heat, viscosity goes down and there is a greater probability of leaks when that happens.
That said - while vendors will dilute their VG before using it in a mix, some DIY users don't, and adding pure VG into a mix without first diluting it with either H2O or PGA is a good way to clog up attys.