Doesn't look that bad for the current bid price. The scraped tank gives a bit of credibility to an RD04 - more rally-like. Other than rotting wheels, stuck choke plungers and the well-known TA/AT tendency to ruin the output shaft seal/bearing if the chain is overtightened, I can't think of any specific RD04 problems, though there must be loads of info on http://www.xrv.org.uk/phpBB2/viewforum.php?f=1
RD07s have the dreaded fuel pump problem and short-lived rear wheel bearings, and they seem to rust quicker than earlier models. This Ebay bike looks strangely familiar. I wonder if it's a London bike.
Tall men see everyone else's bald patch but their own.......