Minor Propshaft play - is it OK?

I'm investigating vibration when travelling about 30mph. Typical suspect, UJs. There is a tiny bit of movement on move props, so just whipped out the rear to changes the spiders. On inspection the spline on the prop itself (don't know the proper name, but the bit that allows the prop to stretch or shrink few inches) also has some minor wear. How much? Can feel it when I counter twist the two halves, but barely see anything with the eye. Fractions of a degree. Is this OK or is it new prop time?

There is a 'bit' of movement, like you say, but its very minimal, plenty of grease and it should be fine.

A bit of rotational play is ok, as above fill with grease. Grab prop near the joint and push pull up down side to side, any movement this way not good and it will soon wear out cause unbalance vibration.

Until you feel excess vibes on the over run it should be fine, not perfect but serviceable.
Are all the prop yokes in line?

mine had no grease nipple on front spider it went bad so i replaced it got rid of knock pulling away and changing gear

Have you tried taking prop off and drivng in diff lock to see if vibration goes

I've changed two of the spiders. One was definitely the cause of the vibration, the other one the way out.

Next question. At the end of the props on the spline end there is a hole, I guess to allow air in as you move up and down the spline to fit the prop. One of my props has a rubber bung plug thing covering this hole which I guess is good at stopping crud and water getting inside the prop once fitted. The other doesn't. Any ideas on the part number?