I would definitely change both upper and lower crank seals. But- my experience with 1954 and 1956 big twins is is that if you run a lot of gas (say 45 + gallons) through these motors, inevitably the top seal (either type) leaks somewhat and usually gets fuel oil mix beneath the magneto, about as shown in your photo. Even with new seals and new crankshaft. The key is whether the fuel and oil gets to the points on top of the magneto plate and shorts the points. Then one cleans the mag plate and points and continues to use the motor.
I’d be more than happy to be corrected on this. What have others experienced?
