Mini update. Undid the fill port to see what the levels like and lots of filthy black oil poured out. Looked like used engine oil but smelled reassuringly transmission like.
Also looked like someone has been in there recently as it was wiped clean. Suspect overfilled in an attempt to fix it. The mtl oil I have isn’t suitable so need to get some G052 spec stuff.
Managed to get under the bonnet though as the release cable had snapped so that was a win.
Are we likely to damage the other five gears by still driving it?