There is a later-style oil pan on the 280's that holds more oil - but having said that, I have two 280 SE engines that each have a dipstick that carries the inscription "230 SL". As often is the case, parts were used for later models, if the specs did not change. So probably there is no difference in the functionality of your dipstick for your 280 SL engine and filling it according to the markings is A-OK