Mac Tubes should've worked.
You launch Mac tubes and a viewer list pops up
In Mac Tubes search box type the name of the videos you're trying to view.
Look for your video in the list.
Click on the video.
It should play.
While it's playing there is a gear icon at the lower left bottom of the player screen, a drop down menu appears and Download is the last option that will allow to download YouTube video in the formats that are available.
The available formats are MP4, 720p HD or 1080p HD.
Try each one to see which formats resolutions can be downloaded.
Sometimes not all video resolutions are available for download.
I use this app all of the time for many years in order to download YouTube video.
I have tons of clips and video in iTunes and on my iOS devices.
This should work for you.
Make sure you've downloaded the latest version that works with your version of OS X.