You shouldn't wait on a silicone project. The two part stuff has a very limited shelf life compared to the tubes of calk. Just saying, you should probably not wait too much longer if it's even still good. Be sure you mix it well before you take it out of it's original containers.
Acrylic cracking? It was probably the MEK. Many plastics become brittle when exposed to chemicals like MEK, acitone, etc.
You shouldn't wait on a silicone project. The two part stuff has a very limited shelf life compared to the tubes of calk. Just saying, you should probably not wait too much longer if it's even still good. Be sure you mix it well before you take it out of it's original containers.
You can also use a pure copper gasket for high vacuum situations but of course not for what you are doing in this vid.