Imho spray, tłuszczem przerobisz nubuk na licówkę jak ten człowiek z linkowanego przez Ciebie forum. Choć z tego co czytałem to on po prostu użył pasty kiwi.
Kiedyś pisałem nawet do haixa w sprawie fragmentu o impregnacji butów którą znalazłem w ulotce z butami:
Use HAIX recommended or commercially avaible non-greasy shoe care products and impregnating agents for all types of leather. Do not use dubbin or leather oil.
Dostałem taką odpowiedź od Niemców:
Dear Mr Wojciech,
Thank you very much for your e-mail and for your interest in our innovative product line.
Referring to your email we would like to answer as follows:
With this shoe of HAIX you have bought a product of high quality which is emphasized by special technical features.
Selected materials and best processing guarantees long lifespan and optimal wearing comfort.
Right care is very important for functional shoes. Therefore, pay attention to the following recommendations.
The best thing is to clean the dirty shoes with water and brush. Wet shoes are not to dry in front of an open fire or hot oven and not to "quickdry" near the radiator. The form of the shoe will be changed by this handling. The leather could burn and get brittle. Take the inner sole out and stuff the shoe with paper or use a shoe tree. Afterwards, dry the shoes slowly and breezy. We also recommend to clean the inner sole from time to time with handwarm water and then to dry them again. The inner sole should be taken out of the shoe always after wearing to accelerate drying. You should use usual, non-greasy shoe polishes or impregnating sprays or care products which are recommended by HAIX , but no leather grease or oil.
Leather grease or oil clogs the pores and then the breathability of the leather is no longer provided.
So you can use a non-greasy shoe polish to keep the leather form drying out or cracking.
We hope we could answer your questions to your satisfaction.