My "new, to me" 1973 450SE has 2 HUNDRED & 72 Thousand miles on it, not the 72,000 "original & correct" the seller maintained...
But, "He's in the Jailhouse, now!"
p.s. You have a situation where you need to do some further investigation, but...
You have one of the finest vehicles ever produced to begin with.
The Auto-RX advice was very good: the absolute 1st thing I did with the 450SE was an oil and filter change, 8 quarts of Pennzoil LongLife 15W-40 and 16 oz. of Auto-RX in the engine, drained a quart of ATF and put 6 oz. in the tranny.
After about 1000 miles a complete tranny service (drain the torque convertor, new filter, etc.) & another oil change and filter. Then, after 2,250 miles on the oil, add the 2nd Auto-RX 16 oz. treatment, drive for 750 miles, oil & filter change and I'm done.
I'm goin' for the 1/3 million mile mark, boys & girls!