Dropped it into my local mechanic as i'd done everything I could think of with it.
Turns out that while the tank breather hose was okay, the actual line _inside_ the tank had gotten slightly blocked up (probably when it was chemically stripped) and it's run a few miles since without stalling so hopefully that's sorted it.
Inline filter being the right way round didn't seem to affect anything performance wise so I assume it's either bust (from me running it the wrong way) or doesn't matter. The arrow on it was barely visible (white on white) so I couldn't see it the first few times i looked.
Fingers crossed that's sorted it (though last time it was a full 13 miles before it stalled). I suspect i'll need to think about swapping my Aero style cap with a vented equivalent at some point.
