I've just fitted an FMF 4.1 slip to my 08 WR450. In in the instructions there's no mention of a washer on the rear-most mount for the pipe (near the seat mount bolt). For those who have fitted one, did you use a washer? By following the instructions i've bolted the slip on straight to the subframe - no washer between bolt and pipe or between pipe and sub-frame. Is this okay?