Another thing to consider , unless the light unit was manufactured with HID in mind , retro fit kits are not always legal or are not as well defined in their beam pattern .
Most HID use a lens assy to focus the light source, halogen lamps have a shield in front of the bulb to remove this glare & direct light through a multi faceted lens ( all those little angle on the inside of the headlight glass )
In the Uk retro fit kits will fail the MOT test ( a yearly legal requirement for vehicle safety ) as the reflector cannot focus the new light souce & direct it through the lens assy .
If you can find HID headlights from a later model that fit your motor , then all is well swap & fit away .
Otherwise fit xenon filled halogen bulbs for a whiter light , but expect to swap them more often when they fail .
Oh and the same goes for LED headlight bulbs & focusing/ beam patterns as it does for HID kits
Nothing worse than some halfwit blinding you at night with poorly adjusted lights
BUT i would definately clean any earth points & ALL conncetions in & around headlight assy . My 312 had a spell of burst bulbs , it was the mulitplug on light unit that was making a duff connection . Soon cured & no problems since