My mirrors on my old 260z were in the same condition. If the glass is simply cloudy or has a film around the edges, try gently polishing it with glass polish or even toothpaste on a microfiber cloth—it helps remove minor cloudiness. But if there are cracks from the inside, it's best to look for a replacement—sometimes you can find original mirror elements without the housing on eBay or in Datsun enthusiast groups.