Hello,
just an update, used a punch and a hammer, together with a product called "Rost-Schock":
WEICON Rost-Schock (Spray).
This cools down the material instantly, while inserting its stuff by capillary action, they call it "chemical wrench". The idea with hydraulic fluid and acetone is also very good, will try this next time.
Also thanks for the table with the different fluids and what they achieve .. good bye WD-40
Was able to open it, innards look good. Will oil and assemble it thoroughly tomorrow, and post the outcome.
Thanks all,
Kai