Just looking for some input. I'm assuming I need to have the head redone on my 98 YZ400F due to what is likely a worn valve/seal. When I first start the bike after it has sat for a little while, I'm burning a little oil. After only a few seconds this goes away and there's no smoke. Is this likely caused by a little oil pooling on the piston due to a bad valve or valve seal? I've never had to rebuild a 4T head and would appreciate any advice or info you can offer. What is the level of difficulty for this job for a regular guy who likes to learn and is fairly competant mechanically? I'll have to grab a manual right away. Thanks in advance.