My PD16 came with the BorisFX Effects. Have a look at your Effects Room (F4). In the section BorisFX Image Resoration, there is the effect "BCC Dust and Scratches". Maybe that does the job. There are other effects in BorisFX, maybe the "BCC Remover"-Effect. Have a try.
Now to the harder part: the masks.
I do not know, how to apply more than only one mask to one clip.
1. So put the original clip on track. (You can deactivate track1 to see the mask.
2. Put exactly the same clip on the same position on track2.
3. Select the clip on track2, and choose the mask designer.
4. Put a round mask on your dust spot, feather it out. In mask designer, only your spot is visible, the other part of the clip now becomes transparent. If you have deactivated track1, you see only the mask content, the rest of the image is black, thats transparent.
If you have not deactivated track1, you see nothing, because track1 is visible, where track2 is transparent.
5. Now apply the effect on the clip on track2. That removes the spot.
If anybody knows, how to apply a second mask on the clip on track2, then do it. If there is no way, you have to repeat the steps from step 2, but put the clip on the next higher track, in this case, track3 and set the mask to the next spot.
You can do that as many times as you want (or spots an the clip), up to 99 tracks... Because everything outside the mask is transparent, you see the clip from the lower clip on transparent parts. If they are all transparent, you will see the clip on track1, no matter, how many tracks with masks you have.
Hatti
Win 10 64, i7-4790k, 32GB Ram, 256 GB SSD, SATA 2TB, SATA 4TB, NVidia GTX1080 8GB, LG 34" 4K Wide, AOC 24" 1080