An interesting watch - thanks for posting. A few observations ...
It's had the standard ADS stripped out, and the replacement (spring) suspension looks low at the front.
It's on non-staggered monobloc wheels.
Driver's seat is in a right state and some of the interior trim looks a bit ropey (there's a gap below one of the seat switch panels).
I noticed an orange light showing on the dash when he was on the motorway.
So some of the above might have contributed towards the bargain price.
As mentioned it's had clear front indicators fitted but not the side repeaters (very minor).
"Panoramic hardtop was originally a £12k or £14k extra" ... erm no, around £2500. Wonder why he didn't bother getting it sprayed to match the car?
Interesting comment that he'd owned an SL60 for a week but didn't like it.
For me the fact that it's totally silent most of the time is one big reason why I
wouldn't want a 600!