Financial talk

I had a retainer (in Australia we call them a plate) for 5 years, then braces for 2.5 years and now I have an Invisalign retainer which I had to wear 24/7 for a year, then every night (which I still do) and soon enough I'll be stepping down to every second night and eventually I'm told that I only have to wear them "every now and then". My problem is that my top Invisalign retainer has a minor crack in it (which happened well over a year ago - my orthodontis said not to worry about it), but now when I was brushing it I think it cracked slightly further!! My questions are: *Is the crack OK? *How long will I have to wear them for (ortho said INDEFINATELY)? *Will I eventually have to have them replaced? *Any tips on maintaining them My parents have paid SO much money and we have gone through a lot for many years in regards to my orthodontic treatment. I just want to see the light at the end of the tunnel after so many years! Thankyou, & pls tell me if u r a proffesional.