Bubble in primary seal - help!

[tim the toolman]

With a bubble like that you should have absolutely nothing to worry about. I'm sure you have a top brace around the top of the tank ie a euro race or a plastic brace. These will act as a secondary control in that area of the tank and also just keep an eye on the bubble, it won't just cause a fail instantly it would gradually spread until it caused a fail. 99% sure you have nothing to fear, and if it means anything I work with glass and silicone regularily.