Hi, I have a 2007 Beta 270 & I thought I would change the coolant, while it was draining i removed the pump housing to check for corrosion & found it or maybe not! The damage to me looks more like cavitation damage, why do I think this? I work on jet ski's & regulary see cavitation damage (erosion) on the jet pump units that are pumps just the same as water pumps on trials bikes. Try a search on google for cavitation
Cheers