to be honest if i was you i would sell it privetly, a dealer will probley not want such an old RR or will make a silly offer like £50, it does depend on how much more your willing to spend on the newer RR, if your looking to spend £20-30,000 on one then the dealer would probley give you more than yours is worth in the form of a discount but if your looking at a later classic or P38 then they will probley not be interested, trouble is classics are being sold for next to nothing theses days and theres a lot about, have a look on Ebay that will give you an idea as to what there selling for, yours looks very clean in the pics and its a diesel so that makes it more desirable..
H