Corrosion once started, is never going to stop. The only permanent fix would be new wheels. I would not recommend trying to use any type of sealant on the tire wheel contact area. You could have the wheels completely cleaned, all paint and clear coat removed, and then professionally corrosion treated, this is commonly done on expensive aircraft components, but the cost would exceed just purchasing new wheels. Check prices on wheels from a larger tire store or someplace online like tirerack.com, they are much cheaper than wheels purcahsed through Subaru.
Thank you. Already looked at tirerack, etc. Just wondered if the problem will reoccur with
new alloys and if so how quickly?
Steel wheels are ugly, but seal better, no?
Steel wheels are generally better with corrosion/rust issues. Yes the problem will reoccur unless you change the conditions the vehicle is operated in. I assume your state uses some sort of aggressive anti-ice substance on the roads. This is likely what is causing the corrosion. You can expect new wheels to last as long as the original ones did before having problems start again. One solution is to buy nice wheels and mount summer tires on them, and then buy cheap steel wheels and mount winter tires on them. In this way your nice alloy wheels should last forever as they would never be exposed to the winter conditions. Of course you would have to drive around all winter on ugly steel wheels.