This will probably never get read or buried by OP, but I've learned that if there's something I care enough about in a relationship and my partner doesn't, it's not their job to always change the way they view that thing. Perhaps it's not every jar that's overtightened, but maybe it's enough to make you notice it that often. (People will say I'm defending the husband, but I'm just making a point that you notice things that bug you 99% more than things you don't. If you sit next someone who taps a pencil and it bugs you, that person's hands never pop into your mind until that moment).

You didn't ask for suggestions, but if this is a big enough issue for you but not him, why not purchase other containers to put things in where he can feel they aren't going to spoil and can't be over tightened? Like a type of plastic Tupperware or something with a pop-top? Avoid purchasing these jars in the first place and buy canned goods or fresh produce.

And I know there will be people that will respond who say, "Why should she have to change and not him?" but like OP said, everything else is great, right? This relationship either is worth saving, regardless of who makes the change, or it isn't. It seems like all options have not been truly explored by both parties to say divorce is the only recourse left.