If you decided to pursue the purchase of the boat, you might want to get an estimate from a reputable shop with experience on Raymarine equipment as to what a troubleshoot and repair cost might be. Obviously they will be guessing to a degree since they won't have the radar in their hands to determine the problem.
But if you can get a "probably about $500" or whatever estimate, you could then negotiate a reduction in the boat's price to cover this. We did this on the autopilot that was on the boat we bought that needed "about $500 worth of work" to make it functional. We actually didn't want the autopilot--- we didn't even know the boat had one when we flew to California to inspect and survey it--- and we removed it as soon as we got the boat home to the PNW, but it did provide us an opportunity to drop the purchase price down a little bit.
So if you can do the same thing you can either put the savings toward fixing the radar you have or toward the purchase of a new and better one.
-- Edited by Marin on Monday 12th of March 2012 01:20:16 PM