It would appear that the lamp comes from a VW Camper but these are rare and the only one I could find at a reasonable price was clear plastic and not frosted. So I bought a Capri lamp which is about 1mm wider. Out with a file and change two of the push on connectors (small ones originally) and job done - no more than 15 minutes work and looks the same as the original.

Many thanks for yet another wicked tip Peter.

(Many of the MB leccy components originated from the VAG group). Mick