My 96 NA has done 175,000km. For the last month or so, on startup, I have noticed blue smoke from exhaust. Once running, exhaust seems clean (revved, in neutral). From this basic analysis, I'm assuming valve guides are prematurely worn, but cylinders and rings are probably OK. Apart from sabotage at the garage, the only thing I could think of that may have caused this is a VERY dirty flametrap, which on inspection was so clogged it had blown the small hose (connected to inlet manifold) out of its housing, causing unfiltered air to enter inlet manifold. Has anyone experienced this before? Am I correct in this analysis? Are there change-over cyl. heads readily available for the NA-5? HELP!! Even my old Ford straight six blew no oil at the end of its troubled, 300,000km, life...