Because of some oil on the Burman steering gear housing I supposed that there would be a leakage on the o-ring of the steering arm. In this case it is recommended to fill the steering box completely with Molycote Longterm 00 grease. This is a heavy duty dark grey grease for gears with partially high loads. To open the top cover plate remove the four screws. Two of them have nuts. I my case the steering gear box was already filled with grease and the oil spray came from the oil catch tank in the neighborhood.
