Just to reiterate what Peter brought up: The three nuts that hold the light housing in place are a real PITA! The studs are mounted in the housing plastic and if there is any corrosion of the stud or nut they prefer to simply spin in that plastic- and then you have a real job at hand...

I would do whatever I could to avoid removing the whole housing. I would guess the gentleman that stole your lenses did not leave the screws for you. I'm not sure the replacement lenses will have screws. However if you have replacement screws you might try putting a layer or two of aluminum foil on the screw before replacing them. You might be able to find some stainless screws that are a bit bigger than the original that would take up the extra space in the enlarged housing.

Good luck,
Randy
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Any twenty minute job is just a broken bolt away from a three day ordeal