Extract from Soarer forum.
Headlamp renovating
Now ensure that you have all the little hoses on the back of the light before you start, holes are not good enough, the little turned down rubber hoses are essential to stop water ingress, if your unit is really bad then it is likely just the seal has gone and all the rubbers are there, moderate discolouration is usually hoses, check before you start.
Oven Temperature: about 175-200F for about 4-8 mins.
they will be very warm to the touch.
Start at one end of the headlight, and use a smooth thin blunt knife (not a Stanley knife) an old butter knife and a couple 'spacers' to keep the 'gains' you have made on your way round.
When apart I returned the units sporadically and removed all the old silicon sealer.
Once it is off then polish the inside, I used my own compound (I am a Scientist, whaddya expect!) but Mer is good but what ever you polish with you MUST ensure you 'cllose the surface, PP8 (a type of poly-propylene) is very easy to leave 'open' on the surface, so the more 'yellow' you remove the more essential it is to polish with finer compounds, I used the CLENS glass polish, (£75 for a 16oz can min order 6 cans, it is the best in the World, used by those fanatical Concours guys, the surface of your windows just disappears, if you ever want this stuff I can get it on the QT, £35, I have never seen it in any shops)
Polishing is a long and tedious job, just BORING.
Always polish the reflective surface and the projector lamp lens it will be filthy.
I used a Simplex heated glue gun on its lowest setting with the Ford duo-silicone pack.
When removing the old, note where all the Silicone must go and warm them again in the oven, take them out after 3-4 mins think ahead and beready to do the job in one go, it just means a little fore-thought as to where suports and tools go but will buy you time with warm bits (always a comfort, time with warm bits).
Do the deed and place in a warm room, do not take outside in the cold, warm dry room is essential and place so that any moisture can rise out of the little breather holes. You did take them off before you put the unit in the oven and stored them safely somewhere, right?
And that's it, do it again to the other and the car looks lovely and fresh faced.
Cheap and easy.
(Just like me, as every woman in Newbury knows)
Mycroft