Was an aftermarket bolt in tail light ever available for a 55 Merc? Decent OEM's are between $2 to 3K. That original pot metal didn't hold up well to the elements; especially salted winter roads!
There's a thread on here about Lee plastic taillight lenses, originally made in the '50s but reissued much later. They made replacement lenses for almost everything, and they made a lens for '55-56 Mercs that replaced the whole tailight frame as well as the lens. Find that thread. Edit: My mistake. Lee made lenses for both '55 and '56 (different), and both are shown in the thread I referenced, but they do not cover the chrome frame area.
Seems somebody was selling fiberglass copies for those at one time. You could always french the OEM diecast ones in....