Oh, sorry about that; the car is a 1999 but the engine came from a 1998 donor car. I agree to your possible culprits and first couple of times this happened, I actually landed on the clamp being the most likely explanation and replaced it, making sure it was thoroughly tightened (I do most of the work on our cars myself having grown up in my dads workshop and nurtured this hobby for half a century.) and carefully located behind the spout bead. Next time it happened it was the bead and part of the spout that gave way and broke off. I guess I overtightened it. I then replaced the spout and thought we were all good.
This last time it was only the bead that came off with the hose. Examining the bead, I found it to be quite brittle, actually crumbling…, maybe because it came from the old engine?
You’re quite right about the ventilated filler cap. I didn’t think of that. So, it shouldn’t be able to be over-pressurized.
I noticed there are some ‘corrugation’ on the spout, so I have re-attached the hose and carefully tightened the clamp. If I keep an eye out I should be able to run with this, maybe with an extra clamp for extra safety, until I find a new spout.
Thanks for your input!