no idea bud, i just replaced the whole engine as it was becoming a bit tired. one way to tell if theyve gone will be to have a look at the colour of the exhaust gasses when you first start it, if there's a slight blue tinge to the exhaust gas when you first start it after leaving it overnight then it could be the valve seals, if it is them the blue tinge should clear after 20-30 seconds. i was told by my dad that i might as well just live with it, as it would be costly to replace them. have a look at the oil pressure sender also, its the only sender at the front of the block to the right (and a bit below) of the exhaust manifold, i had a oil problem also and it turned out that this sender had worked its way loose as its on a tapered thread.. Rich.