UPDATE... I agree that it is possible to overbuild and remove the flex factor, but these frame tab mounts are pure junk on the KX5. We are talking 20 year old mounting tab design.
In my opinion, the pipe, its tabs, and the anti-vibe brackets have enough flex to keep things from breaking. What is happening with my bike for example, is that the tabs on the frame just give out because they are just not in the right place for the aftermarket pipe. I believe that the FMF jig that makes the pipes is just not close enough. Everyone I know has to push the pipe up and in towards the top frame mount to get in bolted on. Then the front tab on the frame is too close to the pipe and the anti-vibe bracket is flexed to fit.
I will get the pictures of the front frame tab pipe mount mod on here ASAP so you can see the better alignment. I will also redo the rear frame tab pipe mount so the weak stock sheetmetal tabs will be gone from my bike. When I mount my pipe now, it just slips into the jug and spins freely right up to the top mount. I have ZERO flex or pressure put on any of the anti-vib tabs so they can do their job and not get torn due to the incorrect flexing put on them.
Sly