Unless the engine has a lot of metal rolling around in it, the big ball bearings on the crank never fail. Usually even on a rebuild, you can use them over. Chances a bearing is out are very, very slim.
A "metallic" sound is kind of indifinitive. Squeek, knock, rattle???? Tim might be onto something with the balance gears, but when they go out, I wouldn't describe it as a "metallic" sound. They will rattle and knock. You either need to post a video to YouTube and link it here, or describe it better. Several things can cause noises. I'd say the seal leaking is coincidental. But, anything is possible.
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