Your State DVM has the answer. Your mileage use is typically limited for historic tags. Here In NJ it's 3K per year I think.

The 300E was a great car for its time. A cared for one like this is a great find. Better than my 88 300CE which had 41k on it in 2001.
Rubber will wear out. The M103 motor in the 88 will outlive your interest in the car.
Very limited electronics by today's standards. No coffee cup holder.

Get the VIN and carfax it. See how many times it's changed hands.
Check the leather on the steering wheel for firmness.?

Check this out:
300e

Good luck.