Performance level API Service GL1 specifications. Suitable for classic car gearboxes and gearboxes requiring a single-grade transmission oil. API Service GL1 specifications. Bardahl Classic Gear Oil SAE 90 is a 100% mineral single-grade transmission oil. The chosen viscosity, especially for classic cars, provides constant lubrication under extreme loads. Bardahl Classic Gear Oil SAE 90 contains a minimal amount of additives and is fully compatible with brass, bronze, copper and non-ferrous metals. It is suitable for sealing materials of the time (paper, cork, felt and fabric). The excellent adhesion of the lubricating film helps to ensure minimal wear, even after prolonged standstill. Application field Appropriate for the gearbox and transmission of classic cars requiring a single-grade ge.