I'm trying to remove the fuel sending unit since the gas is leaking around where the fuel return nipple goes through the fuel sending unit flange. I can't seem to get the quick disconnect fitting to release the fuel feed hose from the nipple on the fuel sending unit. I have moved the collar back towards the 90 degree part of hose fitting but the hose/fitting will not pull off the nipple.

Any ideas how to get the hose/fitting off the nipple?

Also does anyone know what kind of plastic the fuel sending unit flange is? I need to seal the area when the fuel return line nipple goes through the sending unit flange since it is leaking. Most glues I have found JB Weld do not work on polyproplene or polyethelene. Does anyone have an idea for how to seal the leak around the nipple?

First try spraying some PBlaster on this. Place your first two fingers behind the connector, one on each side of the fuel pipe, and press with your thumb to compress the connector. Try rotating a little to free the inner seal. The goal is to pull it off.
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See the 700/900 "FAQ" at the menu bar top screen left side.

Thanks for the tips, I have tried many times and still no luck. I have pulled back on the collar, it moves about 1/8 " and then pulled backward on the 90 degree fitting. Even after soaking in PB blaster it won't come off. It will rotate CW and CCW but just won't come off. There must be rust up under it.

If I slit/cut the collar off to get at it better will it ever work again?

I have also tried to disconnect the metal fitting at the end of the hose where it meets the steel line and that fitting is stuck. I'll soak some more.

Thanks for any advise.

From the FAQ section on fuel sender replacement (see that for photo)
place your first two fingers on the back of the cylindrical sleeve on the metal tube, your thumb on the 90 degree fitting, press them together, and pull the fitting off. You may need a little penetrating oil to free up the inner o-rings from rust on the tube.
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See the 700/900 "FAQ" at the menu bar top screen left side.