Hi Stu
Sorry to hear that you've had further problems! Other than what I've experienced for some time in terms of what I'll describe as a "vacuum" in the tank only occurring when the tank is low and causes hesitation on cornering - provides an inrush of air when the fuel filler cap is removed, I've been OK even yesterday when ambient temperatures got very high - was out Photographing on a Vintage & Classic Car Run. I've put the "low tank vacuum" scenario as possibly a blocked carbon breather??? [Still haven't changed the fuel filter]. Your solution seems a bit drastic, but if it's worked well done - we'll see how it goes and hope for confirmation of a positive outcome.
Did you check the old tank for particle build up and check the fuel pump -[run up dry]? I'd have thought more in terms of a wiring connection rather than an intermittent pump - possible poor grounding; better result on wet days? Just a couple more thoughts .....
Rob