If you cannot figure out a way to remove it, then I guess you might just have to deal with it for now. Try keeping both eyes open, like others said, and keep it on lowest brightness. If you get a better finder, then you don't have to use it and you might as well just saw it off.

If you do drill holes for a base, you just want to be careful not to let the shavings fall onto the mirror. It shouldn't be a problem since you have an open-tube Newtonian. If there were a corrector plate sealing the tube, then it would be a problem.

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