I'm about ready to rebuild the top end on my 99 YZ400F. I have a new cam chain, but am wondering if I need to replace the chain guides. Last time I adjusted my valves, it didn't look like the guides were worn, but the chain is stretched. Has anyone pulled theirs out and found them worn to the point that they needed to be replaced? I'd hate to tear into it, and then have to wait 10 days for parts, but I also don't want to spend $100 if I don't need to. Any comments are welcome.