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,
2.5-16v 1990 90,000m Astral Silver
2.0E 8v 1986 107,000m Black