Yes Neil there is a possibility of the valve block leaking internally and we would never find that out unless it was removed from service and bench tested but that's out of the realms of normal folks testing.
The reason I bring up the struts is plenty on the US forums have had similar leaks that are slow and they turn out to be struts, one test that they try is to park it in lift mode then apply jacking mode.
The theory behind it is the bag will be unrolled to a different spot and may stop the drop or make it worse depending on where a pin hole in the bag might be.
It's not unreasonable to see how they are the most likely candidate for leaks, they are the only moving part and they have a fat girl sitting on top of them with countless hot cold cycles on the rubber.
There is also the corrosion point where the brass valve fits to the aluminium canisister, worth paying particular attention to that area for soapy bubble testing.
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Del
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