WOW! You may want to try flush out the engine, if that was in the cooling system, who knows what's in the cylinder cooling jackets, that's pretty nasty stuff there!
Yeah I was and I noticed no water was coming out of the water pump area, so I pulled off the coolant rail and the whole pipe was clogged, and it still it I wasn't able yet to clear it
According to the service manual it is suggested that the water pump is replaced as a unit. The part 19200-ML7-692 is listed for $119 on Partzilla.
The cooling system on my ST1100 was going the same way after 10 years standing; the thermostat was the worst (basically it was dissolving), but I had a couple of pinholes on the radiator as well. fortunately they've sealed and held up fine for 20,000km using some cold weld goop. Once I had a sealed system, I ran some radiator flush suitable for aluminium parts through the bike for an hour, then dumped that and replaced with coolant.