I've gorn orf the SL - the n/a SLK 55 is a much better car for what I want my convertible toy for, and not much slower than the SL55 - and will be even less so with a £300 remap. EBay still notifies me of new listings, and with the approach of better weather the silly asking prices are rising, but the overpriced cars still don't sell. If the 'market value' of the OP's is only £6800, that's a bit of a clue as to why...
So far as "rear window/boot seals/PSE pump failures/ABC issues etc having all been fettled out of the system over time (and) it would be sheer bad luck to experience one of these 'inherited problems", don't you believe it. In the year before I bought my 2005 SL500, in August last year on 111K miles, the previous owner had spent over £5k on the ABC and SBC systems, and I've just had to get the rear window seal done. Thankfully, the roof works fine - touch wood... I've enquired after a few, and almost my first question has been: "Is there anything in the service history showing work done on the ABC, SBC or roof seals?"
If I was still after one, and the OP was asking £14K for his, I'd seriously consider buying it; it looks good, and has had a lot of the 'inherited problems' sorted. I suspect many of those that are cheaper than that will need a fair amount spending to bring them up to snuff.