I don't think it's leaking oil, just burning a lot of it! Thankfully all the electrics seem to be OK, even the climate control and electric seats.
Do your 260E and 190E have leather and/or MBtex? I find the 190s MBtex just as nice as the 300's leather,

Russ

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190E's:
2.5-16v 1990 90,000m Astral Silver
2.0E 8v 1986 107,000m Black 2nd owner
http://www.maylane.demon.co.uk/190esmall.jpghttp://www.maylane.demon.co.uk/190esmall2.jpg