944 oil pressure loss

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Hi , would anyone her be able to assist me with a problem regarding oil pressure loss on my 944 2.7.
I purchased my car 2 months ago from a gent in the Reading area who had owned the car and added 8k miles on clock.
The car had previously been extensively rebuilt, engine and suspension wise by a company in Hampshire area, I do have a report on work done and the car throughout is in excellent condition, infact as good as the one I owned in 93.

Have added about 1k to mileage and checked all fluid regularly, no losses. Yesterday did 75 mk round trip with 3 hr break.
Oil pressure low when engine hot but no light with light flashing when stood at idle, light came on just before completion at traffic light then stayed on for last 200mtr. No unusual noises, engine cooled over night checked oil, looked dirty but no loss, started engine but rattled like a bag of nails,dry cam followers and maybe me.Removed dme relay cranked motor showing 1.5 bar..

Am in Lincoln area would appreciate any help or suggestions.
Regards Paul

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Thanks James,stripped of sump guard today and covered in oil mostly on off side, some I know from power steering leak which I cured a few weeks ago, but lots of engine oil been leaking for some time. Car was extensively rebuilt in 2018 and covered only 8k since so not likely hade oil change, should have been picked up at that point. However cleaned up spotted oil drip on oprv bolt head, removed valve and looks good, has good pressure and squirts oil but o ring flat.
So is that the prob or is it pickup pipe busted.will try to find some o rings first, that's an easy fix.Checked availability and price with design 911, can have 1 by Friday cost 475. My labour is free but pulling stump pan is a major pain. Do yo drop the motor or just the subframe.Will try crank bolt but that looks like all my options covered before big job.
Has anyone tried putting fibre optic camera through sump plug hole to check pickup pipe, just a thought.

Anymore ideas gratefully appreciated. Paul

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Oprv at 475 and I think pickup pipe at 250, either way a ripoff.
Checked crank bolt today,with nothing to lock flywheel I followed US suggestions and put engine in 5th with handbrake on, wound torque wrench up to 210nm and clicked it twice no probs.
With no Oriings of the correct size available I called 911design and have a set on the way for 12 quid that includes ali gaskin ring, wich I have seen advertised at 50 quid. So fingers crossed , just not looking forward to having to drop sump.

Just as we are allowed to get working on our boat this happens, don't suppose anyone wants to swap a 911 for a 1933 classic yacht, just had a 60k refit.