I found a 6-year-old video by Alan Howat (he looked so much younger then) that covers the whole thing - more or less. He's quite funny, ol' Alan.
https://www.youtube.com/watch?v=ewV0i9MqMb8
It looks (and as he makes clear!) like quite a mission to replace that chain - far better to just change your oil on time, like he says. There is also a very helpful comment in the Comments (where else!?) by
@Sergiu_K about not getting any sealant down the hole that feeds oil to the cam chain tensioner.
Although Alan doesn't mention it, it's pretty clear in the video that there's a hole in the bottom of the tensioner "foot". This, surely, is the hole that supplies oil to the chain itself. Since it's coming out of the tensioner plunger, it must be fairly small, so as not to drop the pressure inside the tensioner cylinder, but whether my partial blockage is there or upstream of the tensioner...
The link again
https://www.youtube.com/watch?v=ewV0i9MqMb8
Although it's apparently (Windscreen sticker) not due for an oil change, I think I'll do that first and see if it helps.
Oh, regarding the TechResources WSM - it looks like the way to navigate it is to find what you're after in the Index, then go to that section then manually scroll down the page (or search by section) to find what you're after. There's a lot of great info in there, but the Alan Howat video is the best overview.
Thanks CB for your excellent insights.
