Last December I noticed a strong sign of dust on the Q7 sensor that showed up on my moon pictures. I pointed the telescope to the empty part of the sky to reveal more, and after drastically increasing contrast in PP, it was obvious that there were actually many (1st attached), even though I was only able to spot one particulate when I looked at the sensor surface by my eyes. Usually my trusty Giottos Rocket blower takes care of these, but somehow the dusts didn't budge this time.
No big deal, I used a spare Q7 that evening, and the next day, and the day after, ... until yesterday when I thought it's about time to clean it.
I started by using the blower again. When I took the picture of the sensor (or rather the IR cut filter) under strong lighting, I was like oooohhhh this looks bad (2nd attached)! If you look at 1:1 crop of the relevant area of the IR cut filter (3rd attached), rotate it by 90 degrees clockwise and flip it horizontally to aid your eyes for comparison with the 1st attachment, you can directly identify which dust particulate made which pattern!
I quickly cleaned the sensor by using lint-free wipes, a plastic card cut to the width of the sensor and 99.9% isopropanol (sorry no picture, but this is my usual sensor cleaning kit) and now it looks good under the exact same lighting condition (4th picture) and it will be good for some time.
This was so disgusting it was sort of entertaining to me.
Oh, BTW you can also see a burn mark on the plastic part above the sensor in the 2nd and 4th attachment. This was most likely caused by an adapted lens focusing the sun outside of the Q7's frame even though I don't remember doing something like that intentionally. All I know is that it happened in 2017 and I haven't noticed that anything happened for a long time because the camera continued to work fine and I saw no degradation in image quality. Once I found that this happened, suddenly I started paying attention to where the sun could be even if it is totally outside of the frame.