Does your pump look like this and have a hose barb on the back pointing down? If so, that's the return line.
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My 85 E350 RV has a different style pump, but it has a hose barb for return like that, using 3/8" hose. At the pump, you just shove the hose on the barb and use a hose clamp. The 85 E350's proper return line looks like this. No seals/o-rings, just a bare hose for the pump end and a flare fitting at the gear. The yellow cap is to help avoid fluid loss when changing the hose.
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I couldn't get the proper return line to go on the gear due to the funky bends in the steel line and trying to line it up at the right angle when reaching down into the van engine bay, so I resorted to buying an "Edelmann Hose Fitting 822660" which adapts the gear's flared fitting to a 3/8" hose barb:
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It swivels and allows for super easy installation in such a tight space, and now I only ever have to replace the 3/8" hose and hose clamps if they start to leak. No special return line needed. Just make sure you route the hose away from any hot, sharp, or moving surfaces. In my RV, that's very easy to do.
Here it is installed. No leaks. (Yeah I need to zip tie it up away from the rag joint on the steering shaft)
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(edited to fix me saying pump when i meant gear several times)