Hello. Cars may be a little higher out there, but I think $5800 is steep, for a car with unknown engine noise.

I have found a few around here (86-88 560SEL) in the $3500-$5000 range. I am actually considering a 86 560SEL for $3500 that looks as good as the one you car considering, but I am still unsure about the running conditons of it. I missed out on a 122K mile, 86 560SEL in excellent condition for $3900.

I would have that engine noise checked out by a MB mechanic before I would pay $5800 for it. That could be a high $$$ repair.
Otherwise- it looks like a very nice car.

You said KBB private party value is $5300. A good general rule of thumb is to never pay over private party value for a car.

If you like it- offer him $5000 for it.

Good luck.

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2004 Toyota Sequoia Limited 4wd
1991 Lincoln Town Car Executive
1991 Cadillac Sedan DeVille
1988 Mercedes 300SEL
1972 Chevrolet Caprice Kingswood Estate 9-passenger wagon
1973 Pontiac Grand Ville
(Prior MB's: 1974 240D, 1985 380SE, 1984 190D, 1993 400SEL)