Good luck in finding that left head light! Same thing happened to me. Looked for 2 years even bought one from eBay that had a LH Headlight PN and picture, being desperate I dropped $1675.00 on the light.
When it arrived it was a RH head light in perfect condition, but wrong side of the car. I have emailed, written, called and visited GM Cadillac Motors HQ to no avail.
Sad thing is, granted there was higher production numbers, but the Eldorado has a plentiful supply if parts available.
The Allante, (yeah I know I said the "A" word) still has plenty of parts in the supply chain - the XLR, just a forgotten and ignored product that people are very passionate about. The dealership that birthed my car into the world in 2004 is 1 block from my home in and dreads every time I drive on their lot.
When my left tail light burned out 7 months ago and I had to go on the hunt for a replacement, I set a time when I would have to make the most difficult decision, if I can't find it, I will sadly have to part ways with my baby - First of December, that happened. I took a beating because of a damaged headlight and totally inoperative taillight, despite everything else working on the car and it being meticulously maintained. It was my daily driver so I could not just park it.
Cadillac just did not have our backs with this, which really is not like them to not give a crap - but they are after the younger crowd now - trying to beat the European and Asian appeal. But also what we have seen in that race to beat the Euros, that the values of Cadillac in the resale market have plummeted. Which again is sad to see.
Anyway I digress, If looking for a LH Head light or any tail lights, good luck! So sad to see this to one I think and a lot will agree was the best roadster Cadillac has every produced.