As you know I had the same problem a few weeks ago
I had to change the sump gasket and clutch etc
My pump is okay... i think
Is your gasket leaking at the front left or right hand side? I was informed that this is normal for a BMW and happens regularly
I suppose it comes down to the price of an oil pump.....how much are they and how difficult to fit?
Remember not to leave the sump without oil in it for too long a period as it will be difficult to get the oil pressure to come up again( something to do with a pressure relief valve or something)
What clutch are you putting on? the Bmw clutch is as cheap as the aftermarket ones at the moment £184+vat GBP to be exact......unless you are going for an upgraded one that is....
And by the way it
is much easier to fix the sump gasket with the gearbag out.....
hope this helps
steve