I kinda keep a detailed record of the Benjamin/Sheridan line. As pretty as it is, the OP rifle doesn't appear to meet the requirements for a "Polished Brass" model's production features. Below is a list of anomalies.
1. As previously mentioned, the allen head screws used in the rear plug aren't factory.
2. The serial number is absent.
3. The front plug looks like it could be polished steel and not the factory zinc alloy.
4. In early 2000 they changed the contour of the forearm tip slightly from previous years. The forearm on the OP rifle has that updated contour, yet the last year for the "Polished Brass" Models was 1999.
5. Sheridans with the updated forearm are also stamped "Crosman Corp. E. Bloomfield, NY USA 14443". OP's has the "Benjamin Sheridan, E. Bloomfield, NY USA 14443".
6. There also appears to be some black in the stamped lettering at the front left of the pump tube. Original black finish, polishing compound., or shadows??
So, I'd also be interested in hearing more information on this one.