My 'baby' 87 560SL has about 150K mi. and runs well. Burns a little oil but no smoke and the oil pressure is in the high normal range. The problem is that the engine (which starts immediatly) gives off a deep rumble sound for about one or two (at maximum) seconds. This is truly a rumble. Not a knock or a rattle as you would get with a bad lifter or rod end.

I remember that my 57 Ford had the same problem and it was a bad main bearing. Are 560's prone to this? Can mains be replaced on the 560 without removing the crankshaft. (On Fords you can slide in a new bearing around the shaft assuming the crankshaft isn't too badly damaged).
Sorry to use the 'F' word but it had simlar symptoms'

Appreciate some advice/ thoughts before I start to dismantle things.

Thanks in advance!
Barrie