I have always run RV anti-freeze which is what I was told to run by Laguna. However, I was lax in changing it on a regular schedule to keep it clean as I think it breaks down over time. When I took a look at it in the coolant container it had an clear glob of scum that looked like some type of floating scum. (Very nasty) In addition, I discovered that the hose connection to the out going side of the pump was missing the rubber seal. Which I think dissolved from the anti-freeze and may have been pumped into the spindle over time. Once in the spindle and the pump not working properly as the connection finally disconnected causing the material to sit in the pump and harden clogging it up. (not sure about this but it is what I suspect may have happened)
On the pump I fixed it by elimination the rubber seals and replaced connection components with brass fittings.