I just ordered a replacement for yet another lost in-ear earbud for my Sony mdr-ex51 headphones. If you’ve never used one of these, they are little pieces of silicone that barely fit over a nub in the earpiece. A slight tug, when say pulling them out of your pocket, will send them flying across the floor. I’ve tried securing them with superglue, which helps a little, but doesn’t completely prevent the problem.
Sony sells a replacement set for a hefty fee at retain. Fortunately, you can now get replacements for a few dollars online. Why couldn’t they have simply made the groove deeper, or the earbud a little tighter-fitting?