M10 Oil Pressure Q (Problem?)

[1985_318i]

I have been having a problem building oil pressure at start up. I am running 15w-50 mobil1 as per my Bently manual. At start up it takes 10 to 20 seconds for the light to go out. Any ideas what could be the problem ?

BTW, I had this problem my old cluster, have changed the cluster and it still does it.

 

[1985_318i]

Could it just be a bad sensor? How difficult are they to change?

 

[bad ass v-dub]

You know where your oil filter is right? On the side of the filter can facing the firewall theres a pipe coming out of it, the oil sending unit is on the end of it.