Never really thought about this but it seems that SA buses have a different (and more convenient) oil filler tube/funnel than the one fitted to german-built diesel vans (or 2E conversions etc), no funnel required:
068 115 285 part number, might be SA-specific or borrowed from something else like a VW industrial engine?
E D I T: You would of course need the metal tube companion part as it seals with an O-ring and has guides to keep the filler upright...
1985 Oettinger 3.2 Caravelle RHD syncro twin slider. SA Microbus bumpers, duplex winch system, ARC 7X15 period alloys