Originally Posted by dwoodward
OEM-quality spark plugs are cheap, and you may not be able to visibly detect functional issues. I once found one that would spark fine in open air, but not under compression at TDC.
Sort of like doing a timing belt on a car- most likely you have to muck with the water pump anyway, might as well replace it while you're there, and hey, crank main seals are cheap and you're right there- why would you not replace it?
I completely agree with this. I bought some Irridium plugs for my 955 but after 12K I hadn't noticed any difference in how the bike ran and I wasn't that confident about them going another 12K so I replaced them with new standard NGKs. For the sake of a £Tenner£ it just gives peace of mind.