Smell of diesel from under bonnet on Renault 1.5 dci magane 2 estate 2007

There certainly has to be a leak somewhere if you smell the fuel. It may be very small and/or someowhere you cannot see. It could be something like an injector that has a solenoid issue and leaks fuel into the cylinder after the vehicle is turned off, this is not the best example as I do not think thisis the problem but I am trying to push the point that there is an issue, just not something you can see or find easily.
Often gas leaks will be hard to find because they evaporate almost immedialtely especially if they are small and/or near something hot. A fuel leak is always a danger and could start an egnine fire, so don't give up on finding it. One way you could at least look for it without the eninge heat helping to conceal it by evaporating the fuel from heat. Turn the ignition to the, "ON" position and do not start the vehicle. The sytem will get pressurized by the pump and you may be able to find the leak more easily now that you can put your hand in areas where it is normaklly to hot and the chance that the fuel may evaporate off a hot suface is not an issue. Also, feel around all the fuel connections you can find. You may not see the fuel dripping but you may be able to feel it seeping out of a connection.
Good luck and keep looking.

You are very welcome.
One thing about the return line is that it is the high pressure line. It has around 45+ PSI at least and will leak and/or burst the easiest. If your repair was a shortcut of any kind, you definately wnat to repair it correctly. When you install o-rings, to keep them from pinching use a little silicone spray lubricatn or even motor oil in a pinch, but very little. Also use teflon thread sealant on any threaded fittings. You should go back and do that or it may not leak. However, removing the fitting at a later time may be difficult as the fuel fittings are a soft metal. They do not take much to knock the corners of the hex head.
The clip will be weakened now that it has been bent. You don't want to end up having it blow off on the hgihway and have it get on a hot motor or worse the alternator and start a engine fire. Fuel injection pumps can crank out massive volumes of fuel very quickly.
I am glad you found the leak though, you may just want to do a few preventative tweeks to it.

Take care,

Dr. C