The changes in how today’s reformulated unleaded gasoline burns in a vintage carburetor-equipped engine will often cause it to not perform as it should. These new blends are not as volatile, but still burn somewhat faster than the leaded gasoline of the distant past.
You may think the adoption of aluminum components is the latest thing in the evolution of Mercedes-Benz vehicles, but even so repair procedures have changed substantially over the last decade.
A pushrod selection consideration is the tuning effect of size, length, and stiffness of the components in the valve train. Any part has a natural resonant frequency at which it will vibrate and a point at which a small periodic input or disturbance coincides with the resonant frequency will cause the vibration to increase with each excitation input.