I lost the little black cap off the tip of the lens release lever (see picture) from my ND20 housing rendering it useless (see picture) and a real pain if using a bulky lens like the Nikon 105VR. After a lot of searching I found a number of suppliers of caps of various materials.
The kind people at caplugs Europe (www.caplugs.co.uk) sent me some free samples and the SRC-125-16 did the job perfectly (see picture). As it is longer than the original cap it is unlikely to come off again. Works perfectly and took about 5 seconds to fix.
Hope this helps someone else
david kessel