Welcome to ABS..
After researching this same issue fairly extensively, I've just come to agree with the masses that it (brittleness / squeakiness) is just part of the aging process of ABS and like wrinkles and age spots, is just part of the life of a brick.
I've read anecdotal reports that keeping them disconnected (unbuilt) and outside of the most extreme temp ranges helps retain their flex, pliability and clutch power which in turn reduces the squeak factor.
Happy to be proved wrong!
Ah I see.
In lots of ways your post kind of relieves me, because now I know that there is nothing really to be done so I can just ignore it from now on.
In terms of clutch power though, I just have to comment that these squeaky parts clutch much much better than normal bricks. They are squeaky but they do clutch great!
Thanks!