my 240 has the B230FX engine in it, original to the car, build date 10/1992, but it seems like not all of them came with a the round tooth setup. I was confused as well, but there was a conversation here a few years back about this exact same issue, and seems like the conclusion is that the last batch of 240s with the B230FX seems to have mostly received the square tooth belt, at least here in Australia. Perhaps the sedans got the square teeth and wagons got the round teeth?