I've been wondering about doing a full conversion in my truck to synthetic lubricants. Not just engine oil, but transmission, transfer case, and differentials as well. The thing is, it is a 1996 Nissan hardbody 4x4, and currently, the truck leaks no fluids. I've heard things about synthetic oils causing leaks before, especially in older vehicles, so I'm a bit worried about that. If I were to convert everything to synthetic, would it do anything to benefit fuel economy?