My new hose port arrived last week and I finally got around to fitting it today.
So far, all seems to have been fixed which is amazing. Couldn't be more happy with the outcome really.
I did find when reassembling the side panel of the saw that there was a weird little metal clip, straight along one side and bent on the other, resting inside the housing with no obvious way to attach it. I am usually very careful about making sure every single screw goes back in place (many iPhone repairs have taught me to be vigilant about such things) but I was in a hurry. It didn't seem to affect the cut but it may give me a sleepless night or two. We'll see.
Anyway, all good for now. Thanks to Phil for sorting me out and for everyone on here helping to narrow down the solution.