are you sure it's not a s420v?it's not that important anyway.i bought mine the same way-from a non-mb dealer but i took it to my local mb dealer and had them check EVERYTHING(even compression).it cost me 2-3 hundred but peace of mind was worth more than that.you may still have warranty left-get them to check for recalls and such.maybe p.o. never bothered with those.see what the dealer can do for free(warranty work) and maybe he'll cut you some slack on other repairs-now or in the future
p.s what are they(cars) going for on the left coast?

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'95 s500 (bought for wife but can't bear to share!!!) 125kms
'92 legend 180kms
'88 tbirdturbo(fantastic car-only regular maint.)120kms
'87 mustang gt(gone)
'86 tbirdturbo(gone)
'85 mustang gt(gone-but not forgotten)