I've had a syringe of the first release version of Optimum's Opti-Guard on my shelf in the shop that sat through the heat of summer and the freezing conditions of winter here in PA. I'd guess it was going on 3 years old or so. It was still liquid, and after doing the whole "try to offer a coating in an average market" thing, I had stopped offering coatings a long time ago.
Just a few weeks ago I decided to polish up the failing and fractured paint on the old Buick and try applying this old stock Opti-Guard to it.
One thing I noticed was that it seems some of the solvents may have evaporated through or leached into the plastic of the syringe. I say this 1. because there was a small air bubble in the product that wasn't there at the time I stored it, and 2. because I noticed there was an unusual amount of "grabbiness" when applying the product. Nothing I couldn't handle but just a bit more resistance between the applicator and the paint than what I remember. I always work very methodically using memory more so than vision when applying a coating so application went seamless. I just assumed I had a little less time to apply the product and go back over it to knock down any high spots than normal.
So far, everything seems OK with the product performance and application, glossy as all Hell and super easy to wash. It's nice to see the old neglected Buick glimmering and beading off water again.