Don't forget to the importance of rotating your diet. I've noticed a lot of people end up finding foods they are okay with so they stick to that food religiously. Not a good idea. I'm still learning about this myself but it is wise to rotate your diet as to avoid developing new intolerances.
And Yes, you can develop a new allergy at any time.
It's kind of annoying, but not a bad idea to keep a food journal. Every food is suspect when you feel symptoms, especially with ongoing leaky gut. A food journal can help you identify problematic foods.
If a food causes you problems or begins to cause you problems, cut it out for 3-6 months then try to re-introduce a small amount of it on an empty stomach in the morning.