So then, when the time comes to rebuild our engines the best thing to do is get a good stock rebuild...is that the advice? Although my 240000 mile 5 cyl. diesel seems a long way from needing a rebuild, I like the car enough to rebuild the engine rather than replace the car, when the sad day comes that the old tank needs a new lease on life. Even the relatively high cost of a rebuilt engine is still less than replacing the entire car - replace it with what??? By then, all of the other 240's and 300 W123's will also have mucho miles on them, too (as if they don't already). What else has the solid structure, good handling & braking, and comfort of a W123? Unless the car gets hit, I am sure that with my regimen of car care, the 123 will still be solid and roadworthy. A new or rebuilt engine would give me another couple hundred thousand miles of usefullness, I'd expect. I doubt that I will outlast this car.
Back to the question - is there any modification that can be made to enhance the effectiveness of a stock rebuild? Balancing the short-block? Fuel injection improvements?? What, then???