Steel rim,poor steel/paint ,it had severe rust after 3 years,I de rusted it with a wire cup wheel in the angle grinder,its pitted like a 50 year old gate hinge,guess the leak stems from there.Permeable casting ? remove tire, clean all of the rim paint with a good 2 pack.
Had 2 on beloveds Roomster, in water there appeared to be no leak it was so slow
Good idea,I have a couple of aerosols.Get a can of that puncture stuff.
Who are the companies?Volvo alloys are famous for this...the alloy corroded where the bead sits.
Tyre places don't have enough time to sort it...needs taking home and going.
There's a few companies who will send you a new set...you then send back your old alloys (worked well).