[Moto-Mojo]

I’m not certain why this should add stress but I presume it’s added angle. A six-ball Rzeppa type joint like these use can handle more angle in the lower rpm range of an axle shaft. As opposed to many main drivelines that use them. A good high temp, extreme pressure grease should work but...you always risk some incompatibility issues when mixing greases. I can lead to early breakdown.

You’ll have to remove (and probably replace) at least one boot clamp to gain access to fill it. But you may not be talking about adding. I’m of the mind the only ‘right’ way would be to remove the shafts and boots, completely flush the old grease out repack it was a synthetic grease and replace the boots. They’re relatively cheap and are the only defense from external contamination - the death knell for any Rzeppa joint. I’ll try to get a grease part number.