We have had several detailed threads on this. I suggest you look at these, as a starting point:
https://www.outdoorking-forum.com.au/forum/ubbthreads.php?ubb=showflat&Number=20076&page=1
https://www.outdoorking-forum.com.au/forum/u...amp;Main=6920&Number=34937#Post34937

I think your Greenfield is the early long-shaft type, which is prone to breaking the clutch shaft after very lengthy service. This is the type described by Deadly Dave in the former thread, above. Most Greenfields have the short-shaft design, with the battery relocated to sit beside it. This is the design shown in the latter thread, above. I haven't heard of a clutch shaft breaking on a short-shaft machine, if that makes you feel any better, though it probably won't.