You're right, overfilling can cause damage but not directly. When the fluid is too high, it will get whipped around by rotating parts, and air will get introduced. Air compresses, so the clutch packs will not apply properly and they will slip. That slippage will lead to excessive wear.
See your local parts store for a syphoning tool. It looks like a short, fat tire pump with a hose on the end. Instead of pushing air, it pulls liquid. They are used a lot for rear axles that don't have drain plugs, but they will work just fine through the dipstick tube for your transmission. You might have to make a longer hose to reach all the way in.
Caradiodoc
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Wednesday, April 7th, 2010 AT 12:55 PM