Not sure what is happening with yours, buy mine is clean as a whistle. It was dirty when I first got the car, but after a good cleaning during the rebuild a year and half ago, still clean. I do have a leak, but its at the end of the hose towards the pump or rack, need to investigate. So down there, its crudy and dirty, but all clean on top. Not sure if there is a rubber seal on the lid.
Like all clamps they can get loose over time, mine were, or the hoses get stiffer and expand. The pressure will make it release fluid quicker, which is my problem with the leak.