There is a big discussion on US forum about cleaning front sprocket and how not doing so can affect the operation of clutch slave cylinder and eventually lead to failure. After carefully reading through all the topic, I've decided to give it a go and clean mine. The point is, at 14.000 km's (8700 miles) the area was quite packed up with junk and I only ride paved roads on dry days. It could go up to 20.000 km's without cleaning (12.500 miles) but that would be a limit. The only thing I noticed on mine is that the push rod was completely "glued" to piston on slave cylinder and it is not supposed to.
Anyway, 10 minutes to remove slave cylinder and cover, 1 hour to clean with first removing big parts with wooden stick and then washing all with WD40 and paint brush (took 200ml of WD40) and then 10 minutes to reassemble everything.
Rode the bike yesterday and today and clutch lever feels much smoother.