On my 300se the left beam would go dim after some time , it seemed like i bad ground or a corroded pin , everything was cleaned and reinstalled but the fault persisted.
I removed the ' good' fuse on that section and simply replaced it with a fresh brass tipped one. Fault rectified. I looked at the fuse under a magnifying glass and it became clear why the fault existed . The alloy tip had eroded away with age .I Replaced all the fuses with brass tip ones and so many intermittent faults disappeared.
mak