I have no idea why they call them 20/40/50 silver series in the USA, because they allso carry the Proxima, Proxima plus and Proxima power model designations for the same tractors...
The 9741 has inboard planetaries, the Proxima has outboard bull gears in portals. These are certainly not a weak link, just look at the sheer size of them... And i have never ever heard any report of a reduction gear failure, on neither series. Diffs went out on 16045's sometimes, (especially when turned open to 240 hp) but not on the smaller series.