Just shoot that thing with light grease through the top of the boot using a large hypodermic syringe? I bet even a needle point grease tip would go in there too. There's never a guarantee but works most of the time . I did my VW bus once right through a hole in the boot And it lasted till I scrapped it.
Back in the day (sorry) there was a "plastic" you could introduce into the joint that would take up some play and get you through inspection.
We had it in the garage, but I don't think we used it other than a try once on some junker. On some worn joints the ball neck would be rusted and ready to break giving the unsuspecting driver a sudden re- alignment to some plus 75 degrees - or more. So "repairs" to sloppy or dry joints can be life threatening.
Funny, now that I think of it, Doctors are doing this for knee and hip joints!
Unless your running a shady used car lot (aren't they all?) JUST replace the bad/worn joint.
2014 Nissan Rogue S CVT, OC#10 47272mi-QSUD10W30+5w20 Toughguard Filter; '17 Subaru Crosstrek CVT OC#2 ?? mi-SOA/Idemitsu 0w20 + SOA Filter