I replaced my filters a little while ago, I was concerned about original filters' deterioration, perhaps these will have decomposed over time even if not in use. So I found a newly-produced filter, documented here: http://vintagecomputer.net/browse_thread_record.cfm?id=588&tid=1 But basically 3M Filtrete #0412560 carbon pre-filter cut to match the original, from a tracing.

Bill Degnan wrote: filters' in original, The filter Bill replaced is the external dust filter. While good to replace, this isn't the internal HEPA filter that Michael wrote about replacing on his RK05 drives, and that he found available on eBay. The HEPA filter is inside the drive. It is a filter designed to capture very tiny particles yet still be a minimal restriction to airflow. To get to the HEPA filter, you have to take the bottom cover off of the drive. The filter is quite large, and as mentioned, there are two different types depending on the age of the drive. If they haven't been replaced in a long time, they should be replaced, as they eventually do clog up with particulates. When this happens, it can restrict the airflow to the disk platter area, which can lead to dust particles ending up on the platter, and that can result in head crashes, which are most unpleasant. Sadly, the manufacturer of the HEPA filter stopped making them a long time ago, and they can be hard to find. I do believe some manufacturer was making reproductions of them for a time, but I believe that they are no longer doing so. So, finding the filters today can be tricky. -Rick