thanks for the suggestions! I did upgrade the firmware of the az gti and I tested it yesterday together with the counterweight. It has improved the tracking by a LOT!! I managed to take 25 shots of 25 sec subs of M42 in a window of clouds and the images did not drift at all in the FOV!!
I then took 25 darks, 25 flats, 25 dark flats and 25 biases all new as I tried iso400 this time. I stacked with and without the darks in DSS and found the stacked image with no darks to look much better (after the same processing workflow)
I then tried startools for the first time (youtube guided) and liked the final image so much I immediately bought the license.
Here is the result from 20 lights @25sec iso 400 (had to throw 5 out because of lightnings in the sky.... lol), 25 bias, 25 flats and 25 dark flats stacked in DSS and processed in Startools (with very minor final touches in my cellphone in Snapseed....). NikonD5500, prime focus, skywatcher heritage 130p on AZgti in altaz mode
and here is my result with the same data processed with gimp and snapseed
boy do I want to get more lights on this target..... I wish the weather clears up quickly