Sounds like a blown HG for sure. Which really is not a common problem with these bikes. I'm pretty sure it was from the previous owner like you stated. But that sort of ignorance and lack of care for the bike leads me to believe there is more to it. When you tear the top end down be sure to check everything. Also it had to get really hot to blow the gasket so check the coolant system( clogged radiator, water pump working?) While he's got it apart he might as well spend $170 for a DRZe kit from Advantange Cycles. It would be well worth it.
2004 KFX400,Yoshi 450 bbk, drze kit, drz flywheel, CWR pro-cams, Crasko P&P, custom Yosh header with FMF PC4, FCR39, ESR intake, Leager A arms, GTT modded 450r shocks, GTT rear link, Tag stem & bars, LSR axle, YFZ450 front calipers
2000 Lakota 300, DG excellerator,400ex carb,JB custom intake,Crasko P&P head CWR 335 kit and 390 cam, 400ex rear hubs, kfx400 front suspension, JB custom rear swinger.
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