[skitsos]

That's strange, usually the spark plug change interval for a tuned car is ~20k miles. At what mileage was your ECU flashed with the tune? Finally, when a car is tuned, the reason the stock spark plugs wear out faster is because the stock plugs are designed for the lower heat range, that the car is tuned for, from the factory. With the more aggressive tune, the heat range has now been increased, which burn the stock plugs much faster. You can change them out with the same, brand new OEM plugs, but you will continue to burn your plugs at the same rate, which could end up being a waste of money, and a hassle in the long run. On the other hand, you can get spark plugs with a higher heat range, which will give them a longer life over the stock plugs. I believe there are some tuned M235i's running M3/M4 spark plugs, which are capable of handling the higher heat range. There is also a member on this forum running NGK Iridium spark plugs, which also handle higher heat range. Also, I'm not sure, but since the M2 has a more aggressive tune, it could also utilize spark plugs with a higher heat range, that could be used on a tuned M235i.

EDIT: also, make sure the plugs are the issue first, because 12k miles seems a bit low. Make sure you are also running the right fuel for your flash tune, because sometimes when an ECU is flashed, it is tuned for a higher minimum octane. I haven't changed my plugs yet (I am 12k just like you, and I've had JB4 on for ~8k), but the plugs shouldn't be that much of a hassle to change one the M235i, as long as you have time, and patience. If you don't feel comfortable doing it yourself, you can always find a garage that preferably works on European cars, or BMWs in specific, if you want. If you are worried about a dealership messing with your ECU, then I would avoid them at all costs. I just avoid dealerships in general lmao.