Cleaning the inside of DOT headlights

[john at westcoastgarage.net]

While prepping for a brake and light inspection to revive a salvaged CQ, 
I've been informed I'll have to clean the INSIDE of the headlights.  
They're fogged (not moisture) and the result is they're not emitting 
enough light to allow the test equipment to operate properly.   Looking 
for BTDTs, cleaners, techniques, etc.  I'm guessing they have to come 
out to do this, but maybe one of you knows otherwise.

TIA!  John