These Bosch 4-point had been in since 1999, this was taken in 2014 after a 400-miler following a head gasket change, plugs only replaced in 2017 after some 40k. Back pair (on the left) a smidgen darker than the front pair, rear carb weakened a tad:

August 2023 - NGK fitted in 2017, about 8k since, the last time I would have messed with the carbs would have been after going lead free at that time. Again the front pair (on the right) very slightly weaker but less than before, I'll put half a flat on the front carb this time: