Thanks for the tip Rene! I made sure that they cannot move. Tried the new cooler on the Ring today: although the air temp was ca. 8 C higher, the oil was about 10 C cooler!
It is a Mocal. The long version and 25 rows.
Because it is longer, it is so low in the car, that it gets extra air through the lower air duct in the front spoiler (put a mesh in it).