Do you have a picture?

The screw on cap sounds like it is a long slip style.  There is generally some cork in there to help keep grease in.   Long slip spines generally have "some" looseness to them, but it shouldnt be crazy..

Fyi, i have ran a longslip driveline that had a crazy amount of movement, these were old parts.  The only thing this really did was allow it to make noise while spinning.  Pumping grease in there would make it shut up for a little while, then it would get noisy until i greased it again.



This was back in the day, before i knew better, i made a square shaft.  The cv blew apart the first snow run and i bought a long slip from a local shop.  But you can see the threaded on style there on the shaft on the top.



At work, we use boots and not those screw on style.