Make sure the oilpan has nothing in it that could plug up the pickup-tube screen. Might wanna do an autopsy on the oil filter itself. If you are SURE you heard a difference, then the oil pressure sensor is unlikely, but i'd want to cover all bases before taking that pan off...specially if your pump behind the timing chain cover like mine is! I've only heard of one MB oil pump going...they are so dead simple, just two gears, failure is almost impossible.

cheers,
dan r.

ps. lay the bolts out on a piece of cardboard with an outline of the oil pan on it...the bolts will likely be different sizes, so you don't wanna just toss 'em in a coffee can.