In coordination and permission with the formlabs support we performed the cleaning of the inner mirrors (including galvo mirror). We received the instruction for that from the support and followed it strictly step for step.
After it we printed the optic test that showed much better results than before the cleaning (see pictures below).
Had similar problem like you and model. Today I cleaned mirror. It had small fine dust on it but small amount. But there is problem because IPA when dry you can see it on mirror when you pass light? I am not sure how to remove that? Going slower with pec pad makes it less visible. Didn’t clean galvo mirror, It is behind and under so I think its not that problematic at this point as mirror. Now its test printing we will see.
We had to use Acetone for a final cleaning step because of this. Seems that most of the commercially available IPA has some contaminants that pose a problem when cleaning optics. There is, however, some kind of “optics grade” IPA available at some sellers, that could be worth a try.
Then I opened again cleaned galvo mirrors closed from side and then opened again from top glass and cleaned mirror again. This time I was 20-30 seconds using PEC PADS in one direction from bottom to top, put ipa in middle of PECPAD and put it on towel so it just leave moisture on pecs. So when you draw this slowly IPA that stay on mirror was soaked with PEC and leave far less smudges. This is how new test optics look
For cleaning the optics, we always had to use acetone, as it doesn’t leave a residue. There should be “optics grade” IPA too, but we never got around to order some. With acetone, of course you have to be careful not to touch plastic parts inside the printer.