Q: Transfer music from Mac to iPod

Each time iPod is recovered

Does that mean you did a Restore on the iPod already?

then continue and sync selected songs (one only each attempt as a test)

Does that mean you are manually dragging songs to iPod in iTunes? 

no track appears after ejection

Does that mean, when using the iPod, it does not show any songs are on iPod?  If so, did you get any error message to indicate songs were not loaded on iPod?  When viewing the iPod's song list in iTunes (with iPod connected), do you see any songs on iPod?

Tried to repair disk via Mac disk utility using mount/unmount icon - message is "unable to unmount volume for repair"

If iTunes is running, try quitting iTunes and then run Disk Utility.

For (1), you are clicking the Restore button, correct?  And iTunes goes through the process of erasing the iPod and reinstalling its software.  But this happens every time you connect iPod.

iTunes prompting you to do a Restore every time is odd.  It's possible the iPod's hard drive is faulty.  One thing you can try is to completely re-intialize (reformat) the iPod's hard drive using Disk Utility.  This goes one step further compared to doing a Restore in iTunes. 

NOTE:  I'm assuming your Mac runs El Capitan (current OS X), with current Disk Utility version.  If your OS X is older, please post back for modified procedure using old Disk Utility.

Connect iPod.  With iTunes not running, run Disk Utility.  Select iPod's drive (not volume indented below drive) in Disk Utility's sidebar.  Click Erase, to bring up the setup pane.  Set it up like this

Name - (does not matter)

Format - OS X Extended (Journaled)

Scheme - Apple Partition Map

After confirming correct drive (the iPod) is selected in sidebar, click Erase.  It should take less than one minute to complete.  Then quit Disk Utility and run iTunes.  Your iPod's hard drive is now blank, so you must do a Restore (from iPod's Summary settings screen) whether you are prompted or not.  After Restore completes, try syncing again to see if your issues are resolved.

You didn't need to upgrade your Mac's OS just to do that procedure.  I could have described how to do the same thing using the older version of Disk Utility...    But If you were planning to upgrade at some point, I guess it's a good a "nudge" as any.

After quitting Disk Utility i then recovered the iPod in iTunes

That means you did a Restore in iTunes, correct?  You clicked the Restore button on the iPod's Summary settings screen in iTunes...?  And after iTunes does its thing, you get the screen in iTunes inviting you to "Get Started" with your iPod (like it's brand new).

the music menu is completely empty

After selecting Music, are you selecting Songs?  Is that where you see that it's empty?

If you show the iPod's song list in iTunes (while it's connected before ejecting), and you see the songs are there, I don't think you have a faulty USB docking cable.  A faulty docking cable would cause some type of error while syncing, or the iPod would not appear in iTunes at all.

When using iPod, use the Shuffle Songs command on the main screen (or just press Play/Pause button).  The iPod should start playing its songs if they are present and seen (in some form) on the iPod.  When you do this, does the iPod play any songs?  If no songs play, what (if anything) happens instead?

So, iTunes sees the songs on iPod, but iPod's onboard software cannot find those songs.  Normally, I'd say there's data corruption on iPod so you should do a Restore using iTunes to clear that up, then re-sync.  But you already did that step.

Therefore, issue may be iPod's hard drive.  It may be faulty in some way.  Since it still seems to Restore and then re-sync in iTunes without an error coming up, you can try a procedure that goes one step beyond what's done during a Restore.  This involves completely re-initializing iPod's hard drive using Disk Utility.

NOTE:  If your MacBook Pro does not run the latest OS X (El Capitan), please post back.  Procedure is a bit different for the older Disk Utility version.

Run Disk Utility with iPod connected.  iTunes should not be running.  Select iPod's drive (not its volume indented below drive) in Disk Utility's sidebar.  Click Erase button to show setup pane and set up like this

Name:  (does not matter)

Format:  OS X Extended (Journaled)

Scheme:  Apple Partition Map

Confirm you have iPod selected in sidebar, and Erase.  It should take less than one minute to complete.  Quit Disk Utility and run iTunes.  iPod's hard drive is now completely blank, so you must do a Restore (whether prompted or not).  After Restore completes, see if there's any difference regarding this problem.

1.  You're OK to eject it either way.  The key point is that the Mac's system no longer has the iPod's disk mounted, before you physically unplug.  I use the Eject button in iTunes.

2.  When the iPod's screen says "OK to disconnect," it should be fine to disconnect it immediately.  That "bar" may be the iPod doing required internal processing before showing its "home" screen.