So my youngest son decided to take my DK-21 to soothe his teething woes today and there goes my rubber eye cup! It was one of the routine cleaning exercise I did today, whereby removal of the eye cup is mandatory to reach the recess area below it.
Cleaning quickly turned to something else and to replace that, I decided to visit the local Nikon service center to get a replacement - DK-21M. It sure makes a difference as you get a magnified view of the viewfinder.
I have not really found the need to readjust the diopter dial and has it for too short a time to comment intelligently on it. Anyway, it does protrude out more than the original eye cup, giving me less need to press my greasy noise onto the LCD panel. Will give a full review shortly...
I got mine for $25.