Original filter removed from the rear card cage opening of the Digital RK05 drive.
After a few aborted attempts Dave G helped me take apart the PDP 8e system so it could be de-racked and moved into the basement. Finally. Before I re-cabled the drives to the computer I decided to replace the filter in the back of each drive where the cards are connected to the cables. I went to the local hardware store and bought general purpose filters, then cut to fit.
If you're replacing your own DEC filter the product I used is 3M Filtrete #0412560 carbon pre-filter