When I was figuring out my own gluten intolerance I found that cutting out obvious gluten was enough to see improvements in my symptoms but they didn't clear completely. Once I got some advice from here and other bits and pieces on the internet- I completely stopped all gluten for a month and saw a lot of improvement. Last month I started to see how much I could have without a reaction. I found that I could have a single kitkat mini bite with a slight cramp and nothing else. So the next week I tried two of them (they are about half a cm cubed once you eat the chocolate off it). That caused the usual problems. So, I don't have to worry too much about cross contamination but it's not worth it to eat obvious sources in any amount. So as Dixiebell suggested go completely gluten free for a few months then reintroduce in small amounts to find your threshold.
Just because you don't react with obvious symptoms to small amounts of gluten does NOT mean you 'got away with' eating that. You could develop any number of autoimmune conditions which are related to gluten intolerance (like RA, MS, thyroid problems, sjogren's, lupus, etc., etc.). Of course your doc won't tell you those are related to gluten consumption, but you will get symptoms of those conditions if you continue to eat less than your 'threshhold' amounts of gluten. If you obviously react to gluten at large amounts, you will still react to smaller amounts, but you may not recognize your symptoms as gluten related.