bike has done 6000 miles, when I bought it, 5400 miles, unkown to me it had badly corroded chrome stanchions, the middle owner didn't care about it cos the level of general corrosion indicates it was ridden and not looked after, initial owner a young lady did look after it. dealer i got it from fitted 2 sets of seals before replacing the the stanchion, it appears they didn't replace anything else so it has just failed as worn bushes caused problems, as long as you keep the chrome stanchions clean and free of pits, seals should last 12 to 15 thousand miles I think, possibly longer.
oddly the pitted and manky stanchion didn't leak but getting a new one and forks set for my fat arse LOL