Our 1992 26/28 fly has below and top steering. One engine has a hydraulic steering pump with a reservoir. USA text on it so I suppose it is original (?).

The steering is not much fun, lots of play (have to turn with nothing happening in between from left to right) so I suppose (from comments elsewhere) that there may be not enough oil in the system.

Here's a picture of the steering column up top. You see the dials have been replaced at some time in the past, they don't show much realistic values (RPM, temp) but do show relative values (I mean: they move and at high temp the temp indeed shows high. But the RPM values are off. I see no adjustment possibility so I suppose they chose the wrong type for the Volvo tacho pulses)
is there a filling possibility there? Is there another procedure to this issue?

Do I fill it with the same oil that is in the reservoir at the engine? Sounds logical to me but I expected that reservoir to also keep the system from developing an air bubble up top so I might better ask first and tinker later.

Drives have no play, piston behind the engine and the rods are all tight (enough) so I ruled those out as causes.