The serial number is the only way to determine the year of manufacture. According to the serial number 7075525 it was manufactured in 1974 and is a straight 850 (no letter series designation).
I believe the D on the data tag simply designates “Diesel”. It does not designate that it is a D series. The D series machines were manufactured between 1984 & 1991. The machines manufactured in 1988 had serial numbers that started with JAK.
I don’t buy and sell equipment but I seriously doubt the machine is worth anything near $18,000. I would guess something closer to 6000 – 8000? Check the value with a Case dealer; they only need the serial number to give you the book value ranges.