The main problem revealed by initial running was a fairly sizeable oil leak. Or leaks.

Not quite a gush, but more of a drip than a weep, if you know what I mean. Seemed to be coming from the oil cooler area:

I had lazily / optimistically just bunged the original oil cooler back in, cleaned but not pressure tested, so the cooler seemed the first likely culprit to check.

Following a modest investment in a Stomski Racing pressure tester (and yes, I do realise there are cheaper ways to achieve the same result, but I can never resist buying another slightly obscure tool...), the result: nope, cooler is fine:

So having established that the cooler itself was probably not the culprit, I disappeared down the rabbit hole of internet wisdom about the cooler-engine seals. Long story short, there are various types:

...and many folks believe that not all types seal properly...

http://forums.pelicanparts.com/porsche-911-technical-forum/795980-oil-leak-dilemma-part-2-damn.html

So I got all excited thinking this might be my problem.

I sent this pic to Barry....

... and proposed that the pattern to the left of the large hole suggests that one of the high pressure seals (at the top, out of shot) has leaked, oil has ended up in the recessed area of the cooler, and made its way out via that blackened channel. Not necessarily during my ownership.

Barry was, as usual, the brains of the party. He pointed out that my leak happened even when turning over on the starter to get a bit of oil pressure before the first run. So at very low oil pressure, maybe 10psi. He wasn't buying my failed seal idea, and when I switched on my brain I had to agree.

So I ordered a new set of seals from my OPC, on the basis that I might as well replace them and the Porsche ones were the most likely to work. For the record, Porsche sent the green type. Many thanks to Paul at OPC Guildford for delivering them FoC. A quick go in the ultrasonic cleaner, and then the cooler went back on the engine: