I am looking to make a liquid starter like I used for about 10 years
before it was neglected for a long time and no longer revivable like
it had been before.

I'm not talking about a runny doughy type of starter, but a true
liquid one. The liquid had in it water, some sugar, some instant
potatoes, and of course, some left over starter from a previous time.
You used roughly 1/2 the liquid in your recipe and replaced the water,
sugar, and instant potatoes to top off the container. I used a
Tupperware type container with an airlock to keep the starter pure,
but I don't suppose that's all that important and letting local yeasts
and lactobacillus bacteria into it might not be a bad idea.

Anyway, will any of the sourdough starters available for purchase work
with this setup, or do I need to stick with the "Amish friendship
bread" type starter I was originally given to make a liquid starter.

What I really liked about this starter was that it didn't turn brown
or black and moldy like a dough type starter when left alone for
several weeks or months. This would last for months at a time without
problems, as long as I would put it through at least one feeding cycle
before using it after an extended stay in the refrigerator.

I did get a starter from someone here named Igor, and it was a decent
replacement for what I had been using. It kept it going a year or so
longer before that died from neglect. If he reads this, I hope he can
post a reply here so I can contact him to buy a replacement for the
Russian sourdough starter he sent me before.

Thanks for any feedback on this.

Don