I doubt the problem is in the bleed return hoses themselves. However, I did replace all mine once and for all with plastic fuel hose that I bought at the local parts shop. It's been on my 80 300SD for about 3 years now, with no more leaking. The std MB rubber/fabric hose only lasts a couple years, then starts weeping. The plastic one is sort of a clear/yellow and fuel rated.
Here's something interesting. When I did the replacement, I overlooked the stub on the last injector. This is basicly a short piece of the tubing that has the end closed off, as there is no next injector to go to. Eventually I figured out that this thing was weeping a little too, but I neve payed a lot of attention to it, figuring I'd fix it eventually and it didn't appear to be leaking much at all. Then one day I noticed my MPG was down to near 20. I checked it several times and sure enough that's what it was, consistently. I still didn't think it could be the stub, cause there was no diesel on the garage floor, etc. Finally, one day when it was raining, I happened to leave the car running while I was standing next to it and saw the classic oil sheen on the water. Replaced that stub with the plastic hose, plus some silicone sealer in the end to cap it off. Voilla! Mileage now at 24, which isn't quite the original 26, but then the car does have 110K, so I'm not complaining.