My water pump inner bearing and seal failed and allowed most of the coolant into my crankcase. Luckily I noticed and turned off the engine.
Normally the "weeping hole" will drip coolant and let you know the water pump seal has failed.
However, after 29 years and 119,000 KM the weeping hole was completely plugged, so nothing leaked. The bike overheated and I was towed home.
Left: Used water pump showing weeping hole
Right: Plugged weeping hole
The weeping hole is on the bottom of the water pump.
The inner seal on the impeller shaft failed and the grease was washed away by the coolant.
Then the bearing started to fail, allowing the impeller to scrape the side of the pump.
I replaced the water pump, changed the oil 4 times (running the engine for 10 minutes between each change) , changed the coolant 3 times, check the valve clearances and was off and running!