[yorkie_chris]

Bit rich, your's is quite free flowing setup, are you using split mains?

Can't see the colour of the insulator nose on the front plug, would be helpful.

Also choke plungers the cables not usually the problem, its crap getting into the plunger that does it or the splitter part, takes less muck to bind up there than at the cable. I always pack the spltter, plungers, cables and lever with grease to avoid this.

If its taken 12,000 miles to get to the point of running rough, I'd say it's alright, a set of plugs a year isn't going to break the bank.

Also a bit of copperslip on the threads might be an idea, doesn't seem to be any there in the pics and it massively reduces the chance of snapping a siezed one.