My oil pressure gauge in on zero. l know for a fact you can not drive a car for 3000 miles without oil pressure. l grounded the gauge, and it went straight up, so l assume it is not a broken gauge. l replaced the sending unit, no difference. l replaced it again, just in case l accidentally got a bad part. Still, no difference. What else could possibly be wrong?
All fuses are good.
The lifter is making everything click a bit, but all my cars have had a bit of a lifter problem, never led to any sending unit problems. Both sending units were brand new.

is the connection onto the sender clean and corrosion free?
i'm assuming your engine is not making any nasty noises?

Do u have the right oil filter? Sub was VERY particular about the oil filter because the hot idle oil pressure was so low. (as little as 12# brand new) This engine had a center main problem as well. 1 in 100 was a knocker right off the new car loader. The oil pressure was so low that people complained so Subaru replaced the dash gauge for one that showed lower oil pressure in a better light. You may have an original gauge which took a different sensor.

Good news is the oil pump is easy to fix-right on the front of the motor. And- the mains come in a lot of sizes- so u can custom fit a crankshaft with out re machining.(if it is round in the first place).

The connection between the gauge and sending unit should be traced for signs of a short, that is most likely your problem.

Like you said, clearly you have pressure.