porous wheels?

[Fazerider]

Several months to go down? With that rate of leakage you’d be lucky to spot bubbles during the soapy water test.
I’ve always been surprised tyres seal as well as they do. When you examine a new loose tyre there are usually bits of flashing from the moulding process still attached to the bead. I trim them flush to give a better chance of a good seal.
It's worth checking the condition of the rims next time you get the tyres changed, the alloy can corrode and cause leaks.