Pat Cassity , Jan 16, 2013; 06:30 p.m.
If you have 600 activations and you havent noticed a problem, I think you are in good shape. I purchased mine shortly after it was released and it had a significant amount of oil that could be see at f5.6 and smaller. I noticed it on the first 10 shots out of the box. Since I cleaned the sensor, I have accumalted about 2000 activations and it hasn't been a problem.