I have made the same bad experience with the Dynarette. After a short while the shellack sides of my guitars got really dull and worn out. Luckily Andrea Tacchi gave me a small bottle of his polish (not the shellack) and a a cotton pad to rub it in. From time to time I treat back and sides with some drops of the polish and it is amazing how it cleans up the surface. Looks like new afterwards.
Giovanni Tacchi, Bouchet model, spruce/BRAZ, 2018
Giovanni Tacchi, Daniel Friederich copy, cedar/EIR, 2017