[Mgs] oil pressure delay question

[Duvall Video Productions]

I've seen the subject of delayed startup oil pressure on here which I have
been experiencing on my 65 B.   I have had to turn it over without the choke
but it takes quite awhile to build up pressure-  15 seconds or so on running.

I'm using a WIX 51374 oil filter which is the filter for an the 75-80 B and it
fits nicely with the oil cooler and adapter.

This filter has the anti drain back valve and WIX filters are supposed to be
very high quality and use a teflon drain back valve which is touted as
better.

Any other causes of a delay in oil pressure?  I thought about it just being
air in the line but the knocking precludes that.