Updating this since I keep seeing recommendations for Outdry, and indeed keep recommending them myself, mainly since no-one else seems to have had this problem.
I was reluctant to try and press Columbia for a warranty replacement, as the chances of them doing that seem slim, and I don't really want to be without the jacket for any length of time, or send it to them only for them to refuse and charge me to send it back. So I finally sent them some photos with no mention or expectation of a warranty situation, to see what they say about why it's happened, and whether it's likely to happen if I buy another.
This is one of the photos I sent them. As you can see, it's got considerably worse since my last post, and I haven't got round to seam sealing it, since I was pondering sending it back.
Their initial reply was:
Over the years, due to the thermal phenomena, the characteristics of the membrane can begin to deteriorate: this ageing phenomenon is unfortunately natural and explains why the jacket is now damaged.
They suggested I buy a new jacket, and offered me a 20% discount code as goodwill.
"Thermal phenomema" to me sounds like "we don't really know what's wrong and/or we're subtly pushing the blame onto you and using some technical words so it sounds impressive", so I pressed them for more details. Is the suggestion I'd let the jacket get too hot, or too cold?
I will better explain what I meant for thermal phenomena, for example if you leave the jacket in the back-sit of a car behind a window when it's sunny, or fold it when it's not totally dry and as well use softer to wash it.
I mean I've probably left it in a warm placeto dry on occasion, but never in the sun for days, or anywhere really hot (it drys really quickly, being non-absorbent, which helps in this, and is one of its attractions). I may have rolled it up and stuck it on my seat pack still damp after rain, but never for very long, and if you can't do that, what's the point in having a jacket? Also never been washed in anything other than water, and very occasionally pure soap.
I also asked if a new jacket was likely to go the same way after the same length of time. This one is a "Outdry Ex Eco Tech Shell" which is made out of recycled material, and doesn't seem to be available any longer. I wondered whether this fabric was a bit sub-optimal, given the recycled material, or just earlier in its development, and was giving them the chance to say this, but they haven't answered that part of my query, despite me making clear that me buying a new jacket is dependent on this. They did say
You can follow those instructions for the jacket I indicated you [OutDry Extreme™ Mesh Waterproof Shell Jacket] as well in order to make it last several years.
which isn't very helpful.
So I'm bit in two minds as to whether to buy another one eventually. I've gone radge with the seam sealer, but I don't think I'll get much more than another year out of it, though it is still remarkably waterproof - more waterproof than any other jacket I've had after 4 years, which I suppose should answer the question.
Still keen to know if anyone else has had the same issue, or has got the same amount of use out of one (and what version) without it?