oil filter spring missing? Low oil pressure..

[Hauser]

I've been getting low oil pressure in my series III rover with a freshly rebuilt engine. It's under 10 psi at idle! I sat down to do the oil change today (first time, new owner). It's got the short cartridge in it. Anyhow, after removing the filter and dumping the canister I had something fall into the oil pan, I fished it out and it's like a dish shaped washer.

I did some googling and it looks like it goes under the filter and presses the filter against the block to ensure that oil is forced through the filter and back in instead of just going around the filter. Problem is, I guess there's a spring that's supposed to go under the washer to hold the filter tight against the block. I can't find any spring! So..
1. Can someone confirm I'm missing a spring?
2. Can I get approximate dimensions or a photo of said spring? I have some old springs lying around, one out of a washing machine looks like a good fit, I could cut it to length if I knew how long it should be...
3. Any idea if this would cause the unusually low oil pressures? My hunch and hope is yes, since the oil pressure sender is mounted to the filter canister. The filter is surely going to be an obstruction, I would imagine oil going around it instead of through it is going to improve flow and thereby reduce pressure.

Thanks,

Will

[Hauser]

Well, I cut the spring, put it behind the washer and put the filter on and filled it up. 7 quart sump is really a lot of oil! 7 quarts every 3,0000 miles is going to get real expensive.

Anyhow, oil pressure now is above 50 at idle. So the filter not being pressed against the block appears to have been the cause of the low oil pressure I was getting on the gauge. That or the old oil was impossibly thin (I put 20w50 penzoil in). I've got some 15w40 diesel oil laying around and will probably use that to top up as necessary.

Still, if anyone has a source/part number for the proper spring I would appreciate it!

Will