*Edit*
Found the leak - little area in extreme top corner beside fuse box has some rust as pictured - does not seem to be a hole as such, but obviously enough to let water in - pointing a hose here will have water trickle immediately into the cabin over the large area of interior surface rust.
Scuttle drains are working very well.
Will scrape back, treat, seal for now and keep car pretty dry and level (it usually is).
Will get property sorted before next winter.
*Edit*
Got the interior out getting reupholstered at the moment so thought I would have a look under my passenger carpet (I know I have a small rust hole there from poking around near the Jack points and I suspected a minor leak too).
Anyway, carpet is dry on top but wet (backing foam is saturated) underneath.
What’s more, got a few rust spots that I poked through plus the apparent source of the leak up high - big patch of scale rust pictured…
Seems to be getting in somewhere around the fuse box, hosing all around there however only saw a tiny bit of moisture getting in and the sill drains are working well.
Sunroof drains are clear and functioning well too.
Struggling to see how so much water could get in, although the car has been parked outside the past 3 or so weeks while we renovate our backyard and there has been a LOT of rain.
Guess I’ll keep saving for rust and paint at some point…