If you mean the silver 'thing' my guess would be a graphic equaliser (showing my age here ) The original vent the 'thing' occupies would be more useful.
When this same motor was on ebay a couple of years back I had intended to look it over, diverting from trip up to Glasgow. On phoning ahead, the seller turned me away saying they'd been snowed in for three days and couldn't get out. Says a lot for the RR's capabilities I thought. As we were in a Corsa, we decided not to risk it, but we got through to Glasgow on the motorway OK.
It had a BMW diesel in it, but I knew very little about RRs back then. The Mrs thought it was pretty , but it had sold before we came back south. So it looks like I had a narrow escape, eh?