GSP(?) brand axles (Advance Auto) came with the car, and finally installed them. They work great, other than the problem mentioned. Should I be concerned? I ASSumed it would eventually stop, thinking that they probably just overfilled them.

Anyone experienced this before?

Chalk it up to yet another problem with Aftermarket Axles.
The Axles are supposed to be even Air and Water Tight. Something thicker like Grease is not supposed to come out.

It may or may not stop Slinging Grease till the Gease level is so low that it won't come out any more.

Where is the Grease coming From? If Your Axle has 2 Cans on it meaning each end looks sort of simlar a common leak place is where the Shaft goes through the Can.
There is no specific Fix for that as they are supposed to be sealed on the inside and by their tight fit.
It might be possible to pull the Axle out and degrease the leak area and apply some Silicon or other Sealant and hope that stops the Leak.

If the Axle has a Can on one and and the other End has Bolts going through it you need to remove one bolt at a Time and degrease the threads and the threads in the Axle and then apply Loctite to the Threads and toque them properly. Otherwise they have been know to come apart.

If it is the Boots that are leaking and they are not cracked replacing or tightening the Clamps may stop the Grease from coming out.

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84 300D, 82 Volvo 244Gl Diesel