Thanks for all the advice and help, I’m hoping to get the silicone on this weekend. Maybe I should start a build thread, will see how much time my kids allow for lol.
You've got the right stuff now for sure; I'll just mention that the last few times I have bought Silicone I the tube has carried the same warning, i.e. not for underwater/aquarium use. Don't fret about that, it's just a legal liability thing; this stuff has been the standard for many years and still works as well as ever.
I once had a brand-new tank, I believe it was 54 gallons, that displayed exactly that same strange line in the silicone that yours does. That is not something you did; if you cut into that structural seam it would be as obvious as a cockroach on a wedding cake. I never did figure out what caused that line; I know that I worried and wondered and sweated about it...for 12 years!...and never once had a problem with it. When I moved away, I gave that tank to a friend, and I know he had it in service for at least another 5 or 6 years, and maybe far beyond that.
And now...back to your regularly-scheduled razor-blading and finger-cramping...
By the way...I am also a Canuckistani native; I've always been able to buy GE Silicon I at Home Depot and usually at Rona, and usually at Canadian Tire as you mentioned.
So I contacted aqueon about there silicone and they said it has no expiation date lol, still wouldn’t trust it if it was 5 years old sealed in the tube. I haven’t had any time to work on the tank yet between work the kids and the house Reno’s tank has kind of been on the back burner. I’m hoping next week I will be able to get some time on it.
Usually if the silicone in still pliable, the tube is as soft as fresh, the silicone should be fine. The only way to spoil for it is to polymerize / cure and harden.