Interesting experiences there, Carey.
The one on my 550 has been flawless.
I only had trouble with one, it was on my customer's 550. I took it apart, cleaned and greased it, but it still did that 1 out of 4 times like you experienced. Mike replaced it and gave me the old one. His new one worked perfectly on a CB dual mass flywheel in the 2276 I built for him.
I took it apart again, cleaned and fresh grease, but assembled it with a 6v gear for my FV. It has worked perfectly all season.
I believe that there is interference where the lower bolt/nut holds the IMI starter on. I relieved the aluminun housing on the starter a bit and used a 15mm wrench size 10mm thread nut(old cylinder head nut). You could also just use a socket head bolt.
This interference causes just enough of a shift in the starter to cause it to not engage. Which sounds AWFUL.
Cheers