Hi Wasp,
What you have there is a pretty honest and original machine.
Sadly it is suffering from what just about all Model 45 series 2 Twin Railers suffer from and that is metal fatigue in the front chassis rail. This is caused by under designed strength in the rail and also a lack of maintenance of the clutch assembly. As it's still the original clutch fitted I would say that if you pull the starter rope slowly you will notice that the clutch does not rotate true and thus this sets up the vibration that's caused that rail to fatigue.
I think, and this is from my vast experience that 8 out of 10, 17 inch machines have this same problem and require rectification of either the front rail or both rails. The 20 inch machines all suffer from it and far worse.
As far as your machine is concerned I would repair it and then end up with a better than new mower. Regardless of which mower you decided to purchase second hand you're not going to get out of it cheaply as they all require some form of repairs as that's why people part with them and also they are 30 plus years old. Find me a machine of this age that doesn't require money spent on it and work to be done.
This is a pretty late Scott Bonnar with the engine being built on the 15th Sep 1980, thus the mower itself would've been built just before the Christmas break up in 1980 or at the resumption of work in 1981 at the Thebarton Factory here in South Australia.
It'd be sad to see it wrecked
Cheers,
BB
