You could say it's a regular V12 car which means about 10% of all R129 production, so it's sort of rare. But, then there are only 100 V12 Silver Arrows on the planet.
Let us know how it turns out.
And Hagerty has 'regular' 2002 V12s rated at $17,300, so I'm guessing this one isn't going to be priced like that in the real world (or more importantly - in the seller's mind). The recent BaT auctions (and don't forget the buyer's fee) of SL500s with similar mileage should serve as the baseline here. Adding or deducting value based on features (mainly the V12) condition, maintenance history and needs, etc.