Coolant Overflow Through Overflow Hose

[K6NS2]

Bike: Yamaha FZ6N S2 (2009)
I noticed bike is spilling coolant through overflow hose after hitting around 100C (at that point fan kicks in). This can reproduced just by turning on bike and waiting until it hits 100C. There isn't any white smoke coming from exhaust. Could this be related to radiator cap, thermostat, water pump or head gasket (hopefully not). Thanks!

 

[Gary in NJ]

It is likely the cap. Do you note that the fans are turning on as the temperature gets close to 100C?

 

[K6NS2]

It is likely the cap. Do you note that the fans are turning on as the temperature gets close to 100C?

I'm assuming the same because it looks like it's not in the best condition, but wanted to get second opinion because other ones are thinking that head gasket could be the issue. Would you recommend to buy OEM cap or should some alternative be good enough (found some 'racing' ones 1.1bar 28mm - shipping time is the only reason why I would get something else other than OEM).
Fans are turning on and temperature starts to go down once fan starts to spin and at that particular time overflow happens too.

 

[Gary in NJ]

I think you'd be safe with an aftermarket unit. I'm fairly certain that OEM units are no different.