Great news, as per suggestions from all of you: last night I blasted the ignition barrel with contact cleaner a few times to try and get rid of any crap in there. I then left it pretty much 24hrs to dry out and I've just been at it with some proper graphite powder (not pencil filings 😂, that didn't work) , putting some on the key then sliding it in and out a few times, then repeating a few times. Seems to have made a massive improvement. Enough of an improvement to not justify taking the barrel out, for now anyway. Will see how it goes. Might have to repeat the whole process a few times, but certainly better just now! 🥳
Thanks all for your input, much appreciated.
Have a good weekend 🏍️
Can't work out how to post a pic, but it was WD40 Specialist Contact Cleaner and Kasp Microfine graphite powder I used 👍