Is it time to change spark plugs?

[Dave48]

There have been plenty of horror stories on here of plugs shearing off when someone's tried to take them out.
I'd consider taking the bike to a dealer and asking them to change the plugs for you. Not something I'd normally recommend for such a simple job, but if they've been in there for a decade or so, they might not want to come out without a fight.

If you do manage to get them out gives you the opportunity to clean round plug recesses in cylinder head & make sure water drain passages are clear of crap. Put some copper grease on threads of new plugs. Carefully screw new plugs in to avoid cross-threading (expensive consequences!) & ABOVE ALL DONT OVERTIGHTEN. Just until you meet resistance and then poss quarter turn against sealing washer which is designed to "crush"