This engine is a 103 , I have never seen one go bad , never seen one stretch even at 250k miles. Now if you want to change it to make yourself feel better do it. The 103 motor is one of the most bulletproof motors built by mercedes ( the bottomend) yea the head has to come off every 150k miles but thats ok. Rule of thumb is with this motor , keep it full of oil , change it on time , dont overheat it , and change your coolant every year or at least every 30k miles whichever comes first. This motor is not rocket science it is simple and dependable . And as for heads I have 2 laying around here gathering dust , the older the cars get the more used parts come available and cheaper they are.