I have an early M2 which is supposed to have the same brake assist. I wasn't able to find one, and mine was missing it. So that being said, no luck for me. Even if you did rebuild yours, for safety on the road and ensuring you stop without issue, I'd replace it and make an adapter using the same four hole pattern from the rear mounting bracket. Thats what I did. For how much my track will be around other people, I dont want to take a chance the original style, even if rebuilt, failed because of poor design. Thats my 2 cents.