Nobody looks at old postings so I'm re-entering this one to add this final(?) bit of info. I asked the info line at Prestone about water to mix with their product. Here's the response:

..."Thanks very much for your inquiry. We would consider the order of
preference for water to be as follows:

1st choice: Type IV water- Both demineralized & Deionized.

Next choice: Distilled water

Next choice: Bottled water (like the type at a grocery store)

Last choice: Tap water

Between distilled and softened water- Distilled would be the better
choice."

So I've been doing it wrong (soft water) all these years. No problems though...still, I'm gonna change.
--
Bob (81-244GL B21F, 83-244DL B23F)