I wanted to give the bike a retro look and wanted to use fork boots. After cleaning out the forks and replacing the seals, I measured the lip that the dust seal fit into and it's the same diameter as the 550 and 750's. I bought a set of fork boots and used a piece of PVC pipe in the upper portion of the boot because the 400 forks are only 33mm in dia. There was then the problem of how to finish up the top section of the boot. I tried using the dust seal and it fits nicely over the fork boot top. In the process of fixing up the front end, I rebuilt the brake piston after having to use a grease gun to get the piston unstuck. Works great and here again the forum was there with the information. Thanks once again. I used stainless brake lines and also put a kit into the master cylinder. The forks and the brake pieces polished up nicely and its back together again.