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Dead 2475S2 / 2476S - replaced caps but get LED flash on SET push and no relay with on/off

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My Smartlabs 2475S2 on/off modules and 2476S switches have been dropping like flies over the last few months. No relay click when on/off pressed and the only sign of life is the LED glows slightly and flashes if you hold down the set button.

On 3 separate units, I've replaced the 3 electrolytics in each and checked the diodes but still the same problem. The original small 10uF caps had high ESR and low capacitance values. I get 160v across the main 250v 6.8uF but the lower supply rails (C8?) don't seem to be stable.

Has anyone had similar issues and been able to repair successfully? I was thinking maybe the LNK354GN switcher IC could be faulty but don't want to start randomly replacing ICs if someone has already found another common fault point. I read the datasheet on the LNK354GN  and it says it resets every 650ms when in an overload condition - which seems about the same frequency as the LED flashes when the SET button is held down.

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