Center Support Bearing movement?

[pressonregardless]

Had the rear of my '74 up with the suspension hanging so I could use a little gunk and a pressure washer to take care of some blow back oil and noticed I can move the drive shaft around about 1/2 to 3/4". Meaning, the center bearing is around the drive shaft, however the rubber support seem very loose, not appearing to pass any light? Any thoughts?
Second related question: I changed my rear end oil last week with GL-5 and what came out (I changed 2 years ago) was milky black, creamy sort of? Should it be that discolored in 2 years and about 8K miles? Never driven in rain, so doubt water can enter. Thanks for the help!

[Redline]

I would replace the center bearing. That is quite some motion and it will just get worse, putting extra strain on other components. The bearing in my Coupe was also loose, with about the same amount of play you mention. It would make itself known by sending a thump through the floor if I took off too aggressively in 1st gear, or accelerated suddenly up hill in a lower gear. It became really irritating, to the point that I would wince each time I got it wrong. It also deteriorated at a shocking rate. After replacing it (and generally overhauling the driveshaft) it was a new car*.

* well, 3rd gear still whines and the suspension bushings are still rotten, but you get my point.