I've just bought a 75 3.0 as a project car to do up as a 'fast street' vehicle. As I go over it with a fine toothed comb, I'll fix things along the way.
First question is about the oil pressure sender. I suspect it's not working properly because it reads very low. I had the same problem in my 155, and replacing the sender cured it.
On the 3.0, where is this sender? And what does it look like? I presume it is different to the oil pressure switch that merely gives a warning light if the pressure is low. Same kinda setup in my 155, where there are 2 separate sensors.
On ebay, I see plenty of oil pressure 'switches', but they look too small a unit to be an actual pressure sender. I could be wrong, but don't want to buy the wrong thing.
It's a bugger to get at and requires a modified spanner of some sort and a lot of patience. Even my highly experienced Alfa mechanic doesn't like replacing them. I must try and get a look at the spanner he uses one day.