I read your post that you are able to get the OEM clips for the low beam so I am wondering can you get the 451 plastic headlight caps for the low beam?
I have installed HID on my smart and cut the OEM caps in order to install the harness. However, the passager side low beam is not working now even I put in the stock H7 bulb. The fuse is not blown, so I need to get a set of oem caps for the low beam in order to bring the car back to the dealer to check what is wrong with it.
No problems with lines or filters. Cars after 1999 have nitrile (or other) fuel lines that are not affected by biodiesel.
I change oil at about 6,000km intervals. It's still black like any diesel is but oil analysis shows less particulates. So it's actually lubricating better than with clear diesel fuel.
As far as I am concerned, after 75,000 km of service, there is no downside and plenty of upside to biodiesel. Just be sure to use store-bought biodiesel and not garage-brew.