If repeated blower and wet-swab cleaning doesn’t change the spots, they may not be on the outer surface at all. They could be residue/condensation or debris trapped behind one of the sensor’s protective filter layers, in which case external cleaning won’t fix it.

The safest recommendation is professional repair. Disassembling the sensor/filter stack or removing the low-pass/IR filter is risky and can easily turn the camera into a write-off. Some users do this only as part of specialist conversions such as infrared conversions.

If you accept the risk and the camera is already considered expendable, one very cautious DIY attempt mentioned is to lightly touch the spot with a loop of cellophane tape without pressing. But if the contamination is beneath a filter layer, that still won’t help.

So: avoid stronger chemicals or aggressive scrubbing, because they’re unlikely to solve contamination behind the filter stack and may cause damage. The practical options are professional service, conversion work, or living with/replacing the camera if repair isn’t worthwhile.