The containers are not airtight, they have child proof caps.
I purchased the 5L kit in early 2013. I did 6 batches of around 7~9 rolls per batch, each mixed to 600 ml solutions for my tank.
The 5L kit can no longer be airfreighted.
As I had some left over from previous kits, I recently purchased some chemicals separately as it was more cost effective.
( see the containers still in bags)
I don't know the life of the mixed solutions, except that one time I did a batch over about 5 days and OK.
In the other cases I did my batch of rolls then discarded the solutions during clean up.
The time sensitive chemical is Part C, and it starts to change color on expiry as described on maco web site.
But at more than 2.5 years when I used the last of it, Part C was still OK.
The only problem I have is droplets of the stabilizer drying.
To help mitigate:
1) Hold the film strips with one side downwards and tap on the bench to encourage the drops to run sideways instead of trickling down and increasing concentration as they dry.
2) Add an extras rinse of 50% distilled before the stab, and change that rinse every 3 rolls.
I hope you get success!