Okay so I got what I believe to be a weird one here. First a little back history to get us to the current "POSSIBLE" problem. The bike is an 03 yz450 About 2 years ago and around 100hrs ago now the bike was owned by a close friend. We were out riding one day and his bike seized up, piston to cyclinder. After cooling off it freed up but the damage was done. Opened her up and replaced the piston and rings and the cylinder had light aluminum transfer and was cleaned up with a hone. Okay now she is all better right? Wrong about .5hrs on the bike and bang same problem. Once again tore it down and this time it took the cylinder out with it. This time we took it to a local machine shop to examine the failure and they suspected lack of oil pressure. Sure enough we dropped the screen on the oil tank "Bottom of frame fitting" and it was packed with what we thought was a blown out oil filter like material. We cleaned out the oil system with cleaners, compressed air, and flushing it all with oil. Of course replaced the oil filter again. Okay now it has to be better right? Wrong about .5hrs in and bang seized up again. Okay now were like what the heck is going on. We inspect the screen on the oil tank agin and once again it's packed with stuff. This time we cut the filter in half and inspect for damage. None to be found. So we figured lets tear this sucker down to it's last bolt. Come to find out the clutch basket cushions were chunking off and clogging up the oil system. So this time we cleaned all the oiling system again, replaced the damaged parts and CLUTCH BASKET CUSHIONS and it has been running great ever since. We checked the oil tank screen every other oil change for quite a while after words and no problems to speak of. Now to the present! I own the bike and have been racing quite a bit. Lately the bike has been feeling like it's losing some of it's snap. I have been planing on doing a rebuild any ways but this last oil change I ran it on the same oil and filter about twice as long as my usual interval.(About every other ride) Well when I pulled out the oil filter It was a boring day so I really pulled it apart and looked into it. Guess what I found? The same stuff that was plugging it up as it did before. So I pulled the oil tank screen and guess what it was 80-90% blocked/ plugged with that same stuff. So I pulled the clutch basket and checked the cushions. By the way this is a Barnett basket, So I unbolted the gear and removed and examined the clutch basket cushions and guess what? They were fine! So Now i'm at a loss. I cleaned everything and flushed it all out with clean oil the best I could. I removed the flywheel and stator to try and clean the oil pick up in the case the best I could but to say the least i'm pretty spooked out now! What do you think the chances are a clump of that old stuff would maybe of just let go off the side of the tank and started circulating again? What are the chances that it is something els and what could it be? The color of the material in question is that of a some what clean used oil filter but the texture and consistency is that of say you were to take a skateboard wheel and hit it with a grinder and you took all the dust and chunks of thous grindings and you put it in oil. We if you made it threw all that you deserve an award of some sort but the best I can offer is a like on any comments on this topic and give yourself a pat on the back!