Best to replace the oil level sensor after draining the engine oil. Under normal circumstances there isn't any pressure in the oil pan so the oil level sensor O-ring isn't apt to leak. Check that the oil level sensor mounting bolts are torqued properly.

I don't recall the oil pan drain plug being aluminum. Have you tried using a small pipe wrench to remove it? I would only remove the oil pan itself as a last resort ... that could introduce another set of problems.

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Fred Hoelzle