Biodiesel in old engines can cause gaskets in your fuel pump to start leaking. Biodiesel is much more agresive than regular diesel fuel. For example Mietek's (MB W168 CDI) user's manual says that it can run only on the fuel with less than 5% bio part. And my Berta is the good old diesel and I've read that bio fuel additives that should clean your injectors were a common reason for fuel pump to start leaking. Mixol (the 2 stroke engine that I'm using) is a mineral oil that won't harm any gasket made for regular diesel fuel, and it lubricates fuel pump and injectors, so it suits me
