I am happy with the 9004 replaceable bulb headlights in my car. According to my research, Porsche used a sealed-beam unit (designated the H5) for 1986-1989 USA cars because the H4 was not approved for use in the USA (until 1992). Due to owner's dissatisfaction with the performance and cost of replacement of the H5, they converted to the 9004/HB1 replaceable lamp in a modified RoW reflector in 1990. Please correct me if I'm wrong here, most of the information came from the PEC.
In any case, the combination of replaceable bulb and plastic reflector create a film on the inside of the glass lens that gives a smokey/silver appearance. I found a way to clean the inside of the lens. I removed the headlamp from the car as a unit. I took off the bulb and the humidity absorbent. Then I poured in about half a cup of clean kitty litter. I shook the headlight back and forth for about 5-6 minutes and dumped out the kitty litter. It took awhile to get it all out.
Here is the result:
I hope someone else finds this useful.
Thanks,
Mark