A clue may be found in the A7CA archive digitised parts lists. The one for the 1938 full Girling rear axle (which had a centre which is D shaped) has a filler hole in the side plate. I presume the filler plug doubled as a level plug. You can just see it in the illustration. Publication 1586a.
Many years ago I became tired of the contortions required to fill the rear axle of my type 65. Removing the level plug was easy enough but inserting the oil was awkward - I lacked the 90 degree fitting which would have made it easier. I added a filler plug to the side plate; jacking the car up and removing a rear wheel seemed a lot easier than the previous nonsense and access was excellent.
I wonder if your axle was an "early adopter" of the full Girling filler?
Regards,
Stuart
Many years ago I became tired of the contortions required to fill the rear axle of my type 65. Removing the level plug was easy enough but inserting the oil was awkward - I lacked the 90 degree fitting which would have made it easier. I added a filler plug to the side plate; jacking the car up and removing a rear wheel seemed a lot easier than the previous nonsense and access was excellent.
I wonder if your axle was an "early adopter" of the full Girling filler?
Regards,
Stuart