John is right in that once you clean up your oil then it can again load up with the dirt it shed before. The key to getting control of this is periodic sampling and systematic filtering set a target and any units that exceed the target level for cleanliness get filtered. In the beginning you will be writing loads of work orders but they will reduce over time after several cycles of filtering removes the years of built up sludge. You might set your work order trigger at 2-3 ISO codes above your ideal target, any wear above normal and an oil change for bad oil. This will get the work started on your most critical items. After all you oil is good and the wear is under control you can drop your work order trigger closer to your ideal target level.