360 Oil Pressure Problems

This is an on going story but I would really appreciate it if anyone could give me some advice.

I have a 02 360 Spider, at the start of October (actually at Poseurs run) my oil pressure warning light came on a few times when I was stuck in traffic.
In each case if I revved the engine a bit the pressure would correct.
After this everything looked ok for a week or so.
Then I started to get the problem again, only when the engine was warm. Often when I would come up to lights, put the car in N, the oil pressure would start to drop off to a very low level.
I took the car into the garage and they changed the “oil sender unit”.
This looked to correct the problem.
However it’s now started again, although its not as frequent.
Basically if I rev the engine quite high and then stop the car in N, the oil pressure drops below the warning level.
However if I drive at low revs and then come to a stop, the car is fine.

Before anyone gives any smartass answers, there is no oil leak and the oil level is fine.

I’m just really looking for any helpful comments before I go back to the garage

Thanks

 

Thanks for your help, I'm going to take the car in on Saturday