Rotary Position Encoder

By chance is the original manufacturer still in business? Do you have a part or model number?

The original manufacturer was Litton, Part number SBD43-104-H-1.

Oracle encoder repair 888-994-2001 and if they are not able to help try calling Encoder products 800-366-5412 they make a lot of replacement encoders. Only thing that worries me is if you take encoder off will you loose your alignment.

Before you go hunting, you need to understand what resolution you need. That is to say, you need to know how many pulses per revolution you need and you may have to build or buy an external pulse counter circuit to implement the same functionality of your existing counter. My favorite brand is Sick Stegmann out of Germany. I use one of the DSF60 family of encoders because it is programmable from 2 pulses per revolution to 65536 pulses per revolution and it can be programmed to output the voltage at 5VDC (compatible with TTL logic) or 24VDC (compatible with commercial interface devices). This family can be used as an absolute or relative position encoder which in your case must be absolute. That means that a switch or sensor somewhere establishes where zero lies. Look also for tutorials on encoders. They are wonderful devices for precise control.