Originally posted by Cannikin I would say it's the LCD cover itself. That's the only real way it can get there. The LCD is sealed differently than the other components (not rubber sealed). I'm pretty sure the "sealing" around the edges is just a really tight fit, and if it's off even a little it can let dust in (which can sometimes actually get in easier than water believe it or not). I've seen this happen and get really bad with my MP3 player and old phone (no zooming action there obviously). It took quite a while to notice at first but it got more obvious over time.
A quick Google search reveals reports not only on previous Pentax weather sealed cameras, but on very high end, professional full frame cameras like the Nikon D3s. To sum it up, it's happened to many weather/dust sealed cameras, and upon complete replacement of the LCD cover, it didn't happen again, indicating a faulty original seal around the LCD:
Dust on the inside of the LCD monitor of D3s: Nikon D3 - D1 / D700 Forum: Digital Photography Review.
Exactly right! The pic a few posts (of the K-5) above shows a perfect pattern of dust being blown under the LCD cover. The LCD cover on my new K20D (18 months ago) was leaking dust a bit as the posters here. I am really worried about Pentax QC because when I posted the problem I got very few responses with my K20D. With the K-5 many are raising their hands.
I replaced the seal (thin double sided tape) myself and the LCD cover (better and cheaper than buying protectors!) I felt I would take more time to do a better job. And in fact it has not failed to this day, my LCD cover is air-tight. The real sealing is the cushions around the LCD itself (not the cover). The LCD is pressed against the body with 4 cushions around it to form a seal. The secondary WR seal I call it is the super small and narrow double sided tape that holds down the LCD cover. So Pentax is kinda relaxed about QC and the LCD cover. But who wants dust and even worse water leaking into the LCD cover area. In fact I have changed my mind about it being not so important as water trapped in between the LCD cover and LCD unit is a major problem and can cause major problems (not the least stains on the LCD) if it gets by the sealing around the LCD.
Hey take a look at this post I made before the K-5 came out on my K20D. It as I said leaked as well but few others did!
The below was written long ago! My seal has lasted over two years now! The cover is held on by double sided tape. The tape is not very wide and allows dust to sneak under many times, very normal for it to happen as its just a thin, not super-strong pre-shaped double sided tape... happened to my sealed K20D. The real weather-sealing for models such as mine is 4 pieces of rubber/foam strips around and between the LCD and body, the LCD is pushed against it so its air tight. The LCD cover is for protection, and anti-glare; its also made of polycarbonate plastic as the body. Luckily its easy to remove and in your case since its not sealing very well should be very easy to remove. heat up the tape area just a bit, so the its warm not hot, just a bit warm and pull up on one corner of the LCD cover with a suction cup. You can get them at any hardware and many other places; they are used to hang things up on windows and other uses... I got the 1" cups that have hooks in them to hang things. This hook gave me something to grab and pull up on. Pull up on one corner gently slowly until you have enough room to insert a device of some kind as a screw driver. However I would use a popsicle stick or something else not so sharp, just in case you slip. Now with it off you can blow it out clean and put the cover back down heat it up again just a bit and press around. Don't touch the LCD, only because its kinda hard to clean and starts another project within a project, just blow it out so its decent and put the cover back down. No need to remove the cover completely just open it like a door enough to blow it out. Your best bet is to order a new cover and pre-shaped two way tape, or at least the two way tape. The parts are cheaper than you can believe. Carefully scrape of the old two-way tape from the flange, clean the flange and old LCD with (your choice) but don't drip any fluid onto the LCD and apply the new tape and your LCD cover. The parts were so cheap I ordered a few of each. I was using screen protectors and don't use them anymore. The LCD cover is pretty hard and mine is not scratched after over a years heavy use... I also must have sealed it well as nothing penetrates the seal around the LCD cover now. They way I knew I had a leak before is as you I had dust in it. One day using a bulb blower one the back I noticed the dust move under the LCD cover... not good at all! So I knew I had a leak. I was under warranty and thinking of sending it in. But I am the type who feels (within healthy limits of course) I can do the job just as good if not better as I will take my time and make sure its perfect. As I already opened the cover, there was no point shipping it in ... BTW my strong advice is to send in the unit ASAP. If you think you can DIYS OK... but if I spent the money Pentax wants for their stuff now, it will be fixed on their dime not mine like last time.