all i know is this, if it helps. i had a 1987 560sec that probably only was driven 4,000 miles a year. it probably never saw 55mph.
i took over its driving in 2000. when i started driving it my way, its oil consumption was similar to my hard-driven 560sel that did approx 20,000 miles per year. within 4 months of daily running, i found it blowing huge clouds of white smoke upon pedal to the metal acceleration after decel or from rest. lube oil consumption was about a quart per 500 miles.
pulled the heads. saw all the evidence of an engine never used. thick gummy carbon deposts on piston crown and valves. scuffed and scored cam lobes. totally deteriorated valve stem seals.
cylinder walls were good.
cleaned piston crowns. replaced valves, guides, stem seals, cam shafts, timing chain tensioner.
since that overhaul, i have put 30,000 high speed miles on the car. engine is tight. lube oil is changed at 3,500 mile intervals - virtually no oil consumption during this interval.
morale of the story: engines are meant to be used. fix the engine. you'll love the car.
next time, though, rent a bore scope. pull the plugs and examine each cylinder before making the purchasing decision.