Since BMW changed the grille design around the headlights in 1972 and again in 1974, rain water or car wash spray can flow past the headlamp housing and, in the case of QI lights, seep past the bulb dust shield and into the reflector area.
Not that much moisture will condense on the inside of the lens but over a period of six months or so the high beam reflector will start to rust.
Do what the Europeans do. Tape the dust cover and the rubber or plastic boot to the back of the reflector in order to seal out the water.
Use racers tape or wide electrician's tape, and do it before you install the lights.
Don't touch the bulb. Just a trace of oil from your fingerprints is enough to make the bulb burn out prematurely -- like in five seconds. If you have touched the glass, clean it carefully with rubbing alcohol. Once you have driven with quartz iodine or quartz halogen lights, you'll wonder why we still use sealed beams with their inadequate and poorly directed illumination.
Author: Warren Markey