About 18 months ago from our 3 R44's we had ring gear problems with 2 of them and after replacing the ring gear found similar teeth stripping and slipping as you have mentioned.
Probably only got 300 hours from the new set of ring gear from both choppers, our engineers put it down to mismachined ring gear.
Robinson did not agree and consequently did not receive a credit.
After fitting the replacement set we kept a careful eye on the starter motor nuts (especially the one tucked in behind the starter motor and a nightmare to tighten).
We found the nuts were gradually loosening and we appropriated this to the ring gear slipping problems and since locktighting the nuts and have had no problems.
We have found it most beneficial to change the starter motor inconjunction with the ring gear.
Hope this helps (Our choppers were an Astro and a Clipper if this makes any difference)
