I followed the guide and it worked a treat! I had to drill out the bolt as it wouldn't shift even when blasted with penetrating oil. It's my first time doing this so I was very surprised I managed to get it out with the thread intact.
I've replaced it with a nice shiny stainless steel M8 x 30mm bolt and washer. Looking at past receipts the belt was replaced in September and still looks fine, I've now got a replacement just in case.
Thanks for the help, I really appreciate it.
