2001 540i, 91k miles. Previous owner replaced radiator, tank, thermostat, and hoses within last 6k miles. He can't remember if his mech changed water pump (dumb if didn't) and can't find that work order. I've got a coolant leak, uses 3-4 ounces over a 1000 mile trip. Just enough that it leaves some spots on the floor mid-way back engine (dripping down through oil pan drain access). I'm presuming that the pump has started to go TU. Any way to check and make sure ?? I've changed small block Chev and Mopar pumps over the years and with those it's relatively easy to look down on the pulleys and see if you've got a drip. There is so much stuff under the 540's hood that my old eyes haven't spotted anything.

Questions ....... if replacing should I use OEM or is there a better choice ? Also, how much of a PITA is this to do ??

Thanks in advance, Vaughan