1972 (and '73) are the best years of the W107 SL's.
They have the original euro-style bumpers. The federalized bumpers on later cars look like park benches.
Also, even though 1972 models were badged as 350 SL's, they really have the 4.5 liter V8. Most were changed over either at the dealer or by the subsequent owner(s) of the cars. I guess yours wasn't "rebadged" which makes it cooool.
1972 and 1973 also don't have smog equipment, like catalytic converters, so they make more hp.
I say $6,000 for a clean car is already a deal.
$4,000 is a steal.
Why don't you buy it for John Doe as a gift, or as a trade for free legal services?