I have Wagner steering and rudder angle indicators installed sometime after 1972. I do have a Wagner service manual for "newer" Wagner autopilots (Micro, SE, etc.) that covers controls, power packs, accessories and angle indicators. I could scan pages for someone with issues to solve.
You can find parts, repairs and manuals here for old Wagner steering and autopilots:
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To bleed my system by myself, (the helm pumps are self bleeding), the cylinder has bleed ports where I attach a hand operated vacuum pump made for bleeding auto brakes. Pump up the vacuum, crack open the bleed port. I rebuilt my cylinder and had to vacuum bleed several times including turning the wheels lock to lock to get all the air out. I don't believe the oil has ever been changed. My plumbing between the helms, pump and cylinder is about 70' of dual 3/4" copper pipe. If I have any leaks or trouble plan on changing to hydraulic hose.
The bleeder in the pic is about $20 on ebay. There is a small vacuum container between the pump and rudder cylinder that catches the oil. I use a bigger container for major bleeding. Container can be anything that holds a vacuum with a sealable top -canning jar, gas can, bucket. And you can do your brakes.