Right now you got that sorted, then we can start with the fuseable links, rip them out put them in a bin and fit an under bonnet fuse box from a 300 TDI. A very easy job to do
again that wouldn't cause 1 head light to be OK and the other dim. It's some thing to do with the individual lights, voltage feed, bad connection or earths
Personaly I think it's an earth problem. If the switch was defective the lights would be on or off or dim, but not a combination from left to right.
So I would be checking out the earth points or the plug for the lights, they can melt.