The car in the OP is an F1 spec car (uprated power, brakes, different front bumper and one or two other tweaks). These command a premium over the standard SL55s.
The cars in your links apart form the one in North Yorkshire are 2003/2004 spec cars and have an older Command system with CD based nav and one or two other differences like the centre console etc.
In 2005 (late 2004) the cars were slightly facelifted and the boot seal issue is less prevalent with these. The car was facelifted again in 2007 with a different grille, sills, interior tweaks etc.
Common issues are the ABC suspension system (pump, valve blocks, struts) which is expensive to repair properly, SBC failure (was done under recall, but no longer) - expensive, baffles in the fuel tanks coming loose - expensive, boot seals leaking taking out the electrics in the rear of the vehicle - expensive to do right, corrosion on rear window bottom lip that can cause leaks - needs new window or a good independent to remove, refurb and re-install and rust on rear arches although this is relatively rare. Oh and creaking roof - lubrication sorts most of it.
Aside from that the cars are bombproof LOL!
That said it's one of the best looking cars on the road IMO!