Jim,

You need to disassemble completely the rear scope mount and clean it thoroughly of all old grease and oil. Lightly re-oil with a modern lubricant. NOT 3-in-1 oil! Check the springs in it and maybe replace them with stiffer ones. Your problem sounds like it is coming from the rear mount not returning to it's proper position between shots. You can check that with a dial indicator and the rifle firmly locked in a vise. The dial indicator will tell you whether or not the scope mount is "sticking". Just push the rear of the tube with your finger and see if it returns to the same position.

HTH,

Emri