Well, if it is sealed closed with no way in, then there is no need for cleaning!
If there is a way for dust to get in, there is a way to open it. Those 4 little holes are probably going all the way through the "top" part of the assembly and the "bottom" parts has pins that go into them. You could either try prying them open with a sharp tool or you may need some hot air gun to loosen any glue used to keep them together. That's as far as I can deduct from a picture, lol.
But then the question becomes whether you could put them back together again successfully or not. Based on your question and the looks of it, you probably won't :)
So, bottom line, you can try opening them up but be ready for the possibility that you'll have to replace them with some fresh ones.