1956 Buick differential

There are no drain plugs on the differential cover and the cover is welded on my 1956 Century. So, how do I change the lube in the differential? The shop manual says that the lube does not need to be changed. But, after 62 years with the same lube you would think that it would need it.

Maybe a tube through the fill hole and use suction to remove the oil? Or you can pull your axles and separate the torque tube and axle housing but thats a big job.