I too have had my SA striper lines crack and break up, particularly the smaller wieght sizes, 6wt for instance as opposed to an 11wt. I know when I cleaned and dressed them they performed better. Ye old squeking sounds when the line goes over the guides is a good clue to dress your line.
Twisted sections made my tangle rates go up too. I plan on trying another type of line for my latest fly rod for the intermediate sink line.
My tarpon taper SA has been goood without any cracking for years. It tangles abit in the cold and when it's twisted or not dressed regularly.