If the idle RPM is higher than usual, or erratic, it can indicate a bad LHS or centre (or both) seal. Spraying a little carb cleaner towards the rear of the flywheel while the motor is running will often see the the RPM rise as the combustible cleaner is "sucked" into the crankcase via the LHS seal.
I am a firm believer than modern fuels are very destructive to the crank seals, and it's highly likely they will all need replacing. The integrated centre seal is particularly weak and susceptible to failure on 1989-1997 models.
Unfortunately, if the centre seal is failing it will mean a crank rebuild/new crank, if that is indeed the case. We've seen new [89-97] centre seals fail within just a few years since the introduction of [more and more] ethanol in fuels. (The MC16 & R2/4J doesn't seem to suffer anywhere near as much.)
How do know the lower barrel is running "hotter". Are you simply judging by feeling for the heat differential of the exhaust gasses on your hand once the engine is up to normal operating temperature, or do you have access to in an infra red temperature gun?
A leak down test would indeed be a good idea, but to be honest, I would prepare for the worst. The seals (particularly the centre) just don't last, and if they're already a few years old, and have previously been "immersed" in fuel, I would put money on, at the very least, the centre seal being buggered. Sorry.
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Andy.
NSR-WORLD.COM
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