Based on Andy’s and GIMP’s method I created a spot detection method for RawTherapee way back when.
I just tested these rtc files using ART and they work on that platform too.
That is one dusty sensor 
Depending on the image you do need multiple methods to be able to detect the spots, hence the 4 I created.
Here are the 4 spot detectors in zip format.
Good thing that both RawTherapee and ART have the ability to set 2 Tone Curves…