Good luck with your sale.
At the risk of pedantry, I don't think there ever was an OM-1n MD.
The progression was:
1. Olympus M-1 (rare and withdrawn);
2. Olympus OM-1 (for a relatively short time);
3. Olympus OM-1 MD; and
4. Olympus OM-1n.
When the OM-1 was introduced, Olympus offered the conversion to motor drive capability as a factory service. They had such a high percentage of owners request that conversion that they quite quickly stopped selling the camera in that form, and replaced it with a camera that incorporated the motor drive capability right from the beginning. To help differentiate the versions, they added the MD (motor drive) badge.
When the OM-1 MD was replaced with the OM-1n, they left the MD badge in place.
I used an OM-1 (no MD or n) for many satisfying years. I later used an OM-1n for several years. Both are very satisfying cameras, and the one listed looks nice too!