The bulk of road cars use an inert gas in them, as you say to prevent aeration, but one of the other features of this is it also acts as an air spring similar to an Oleo, although not quite.Since the damper in basic terms is just a piston with valve openings moving though an oil, tell me why they should return on their own if laid horizontal. If held vertical they may slowly extend under the weight of the lower part. Dampers work in compression and rebound with different damping rates for each direction. On my race car I could adjust the rate for either direction.
On the P38 for example the damper is near mid range at normal height.
If your race car didn't extend by itself it was either knackered or a gas-less damper which as the name suggests is gas free and as such won't extend on it's own.