Doing very small amounts of mileage nowadays so I tend to only put in about half a tank. Someone once told me that Shell V-Power (now Nitro+) used to settle and some of the additives fell out of solution, reducing the octane rating. No idea if it's true or not but seemed like a good idea not to have a full tank in there for weeks on end. And yeah, might be close to doubling it's value these days too
