Wow Marc, lovely image indeed!
Strange about how you say you get better results from a highly oversampled dataset... Some oversampling can be useful for the purpose of deconvolution, but if your dataset is already oversampled at native resolution, I would expect a drizzled dataset to be quite a bit inferior in terms of signal fidelity.
Another possible issue with drizzling (unless done very precisely and copiously) is the potential for correlated noise to come into existence. The latter is infinitely more difficult for algorithms of all sorts (decon, noise reduction) to distinguish from detail. As a result such algorithms may have trouble working properly.
To illustrate, thanks to the oversampling in your JPEG, I was able to restore a fair bit of detail from even the processed/stretched 1:1 image;
https://download.startools.org/Tutor...eb_NGC3372.jpg
(detail can be corroborated
with this recent APOD) I can only imagine how much can be restored with the actual linear dataset!
As for the trouble you're having with the star mask; in ST, to create a star mask that includes large contiguous overexposing areas,
Under Mask -> Auto, make sure your Selection Mode includes 'Highlights > Threshold' (e.g. 'Highlights > Threshold' or 'Light Features + Highlights > Threshold').
Then lower 'Threshold' to the brightness value from where you wish to select highlights (e.g. 85.00 would select any pixels brighter than 85% of pure white).
If you got the SII data on the target already, you could consider adding it just for the purpose of coloring, while sticking with the Ha and O-III for your luminance. Color data doesn't have to be amazing to be useful. I for one would be really keen to see this amazing detail in an RGB:SHO/HST palette rendition!

Pretty please?