Y'know, I've owned my 400 for nearly 35 years now, and early this year I replaced the whole front brake system except the disc. Early this week it suddenly developed the previously talked about sound effect of a pig being dragged along by its wotsits. 2nd bike was occupying the ramp so it was a quick 45 minute curving of the 75 year old spine to split the calliper, scuff the pads, and brutalise the disc surfaces a little. Managed this without having to disconnect the fluid pipe, so floating pad was inserted by feel as has been done many times before. I had put the little blobs of red grease on all the relevant surfaces, inserted the two main fixing bolts lightly using a 3/8dr ratchet ready to finish with a torque wrench. Before the bolts were even fully home, the brake was locked solid. Hm. Loosen everything, including the adjuster screw, pivot arm nice and free, using thumb pressure managed to push the piston further in. So, re-assemble, same result!! Rather than attack in temper, down tools, switch off light and go indoors for dinner. 2nd attempt this morning, fresh brain, spine nicely loosened off, split calliper yet again, removed the floating pad, and out fell the white nylon ring 'twixt pad and piston, nicely chewed up! It had obviously dislodged when I inserted pad "blind", and upon tightening the bolts I had destroyed it which meant the pad was sticking out too far. Is it just me, or has this happened to any other unwary person? Oh God I love this hobby! Mike. (PS. Yes I did have a spare one)