Hello, I have recently purchased a 503cx and of course the first thing I do is lose my darkslide. I have been actively searching for a replacement online and other various camera stores local to me and realized that what they only had were which I believe are the newer style of darkslides with the two bumps. I assume those are for locking the darkslide in? The original darkslide I had was completely flat, no bumps, so I am searching for the same one. Can anyone tell me the difference between the bumped darkslide versus the flat? And is it possible to use either or on my back? Thanks in advance!