A Vmod user here... Nice review... My only comments concerning your leakage issues are as follows.... Leakage at the atty or carto is generally caused by over tightening the cone (which it appears you are not doing) or a wet/dirty upper gasket and or atty/carto... Make sure that the upper gasket is clean and dry when assembling the Vmod as well as the atty/carto... Having a good seal should keep the
juice from getting up on the atty/carto...
One other possibility could be the cone itself even though you apparently are not over tightening there has been some inconsistency in the cones themselves... That inconsistency being that some are longer than others at the
threads... If this is the case this would cause more or less a pressure blow out caused by the end of the cone putting to much pressure on the upper gasket even with minimal tightening... Quick fix being just to sand, file, grind maybe a mm off the end of the thread part maybe more or less.... Secondary fix could be a really flat rubber washer/o-ring that fits on the base of the cone above the threads found in a faucet valve seal replacement seal kit from lowes or where ever.... Not sure on the size of the o-ring but it has been mentioned in the "fan" thread...
Hope this helps... And I got it right so I don't suffer AG's wrath....
Edit.... You may have an overfeeding issue going on as well...A heavily saturated carto as well as the leakage would be an indicator... If that seal is not clean the excessive
juice will end up some where....