Why does my 1999 Holden Rodeo engine gush oil?

Based on probability, you either have a faulty oil filter which is not sealing properly, or there’s a crack or some other flaw in the boss (fitting) on the side of the engine that accepts the filter. Chances are the oil appears when the engine is cold and oil pressure is highest. The oil pressure (which all engines need to survive) is pushing the oil out through the weakest part of this assembly.

It’s not unknown for oil filters (especially cheaper brands) to have basic manufacturing flaws that allow them to leak, so that’s where I’d start my investigation.