I have a cracked lens on one of my XK140 FHC side lamps. The complete side lamp assembly (C4517) is available, but I’m pretty sure that the glass does not have the ‘LUCAS 513 MADE IN ENGLAND’ cast into the lens.
I do have an original spare side lamp assembly with a very poor chrome rim and as the chrome on the one with the broken lens is excellent, the solution is the swap out the lenses.
Can the lens be separated from the rim, and if so. How?
I don’t have any extras so I removed one of mine and it appears to have a separate metal ring with a fiber gasket but they don’t appear to be removable. The ring may have had a slightly larger OD than the ID of the bezel and was pressed in when assembled relying on the interference fit to secure the lens in place. Perhaps you could experiment with the spare by removing the ring.
basically not removable they are rolled on as part manufacturing process easier enough to get S/H spare I will have one here if required