I pulled my plugs at the 12k service, only one had anything in the way of watermarks, but I put them back with a good wipe of red rubber grease especially under the cap part. Bikes on 24k now but is sorned for the winter, as I’ll be using my old GS instead, but it will get a service before spring where I’ll be checking valves so will see then how things have faired the last 12k. If I was suffering similar issues to the OP I’d be filling all the assoviated connectors with red rubber grease too. I might even do so when I pull mine apart.