Hi Q
Any chance of uploading a photo or several?
My suspicion would be it's the same issue as I, and many others, have had.
There is a sleeve gasket between the rear down pipe and the collector pipe it slots in to. The original exhaust clamp fails and this allows exhaust gasses to leak past which burns it away to nothing. This will cause a noisy droning exhaust and potentially shocking fuelling and economy. If you have after market cans like mine then it will also lead to nerve shattering explosions on over run
I tried the putty and clamp fix myself for a week long tour I had planned, the putty lasted less than a day so you did well at 4 weeks.
Fitting a new gasket and exhaust clamp will fix the issue if it's the same as mine. I went belt and braces and replaced the forward gaskets as well since removal of the front pipe is required to drop the collector box. Even with new gaskets and full stainless clamps for all connections, my parts bill was maybe £50.
Of course there could be more at work here and photos would help diagnose but, since the exhaust system is stainless, replacing it wholesale seems very unlikely to be needed.