Q. When should I replace the tank o-rings or silicon gasket for the cartomizer positive pin?
A. The o-rings or gasket should last quite a while under normal use, but should be replaced whenever they are obviously nicked or damaged.
Even if damage is not obvious, replacement may be indicated if:
O-rings: Liquid drips or drains from top or bottom of the tank.
Silicon gasket: Excessive liquid "condensation" is consistently found behind, under or on top of the tank.
To be fair, the gasket may not actually be damaged yet. But if you're not getting obvious leaking from the tank, the brass ring may be a little too loose or too tight which can compromise the seal provided by the positive-pin gasket.
Hopefully DD will weigh in on this as well - he helped diagnose the issue when I experienced it early on. It still happens to me from time to time, but I do have a tendency to crank the brass ring down too tight.

