If the nipples are truly damaged or loose there is no way that I have heard of to fix them. If they are leaking from being loose about all you can do is us an aluminum or brass drift a hit them enough to stop the leak.
If there is a big deep scratch on the nipple It might be possible to degrease it with brake cleaner and work a tiny amount of JB weld Epoxy into the crack and after it is good and hard sand the excess of with 400 grit wet and dry sand paper.
Other ideas if the nipples are scored: Degrease as above apply silicone sealant around out side of nipple and put a NEW hose over it and let it sit for several hours on a warm day before you use it, try using return lines of a different material such as Weed Whacker fuel line or 3/16" silicone vacuum line (I had some on my Volvo diesel for a little more than a year; it works but it gets so hard that you cannot use it ounce it pulled off), or how about some Viton return line.

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84 300D, 82 Volvo 244Gl Diesel