The 500 series are giving problems in flax. Apparently its wrapping at the back of the rotors, I was talking to a mechanic yesterday and he was saying they had been trying different things. They untimed the rotors and it seemed to make a big difference. The 400 series were amazing in flax, but it seems to be the new style rotors that are giving the problems, we'll likely be into our flax in another week, I'll let you know how we make out.