Wierd...
In my experience the common place for a squeak is the pivot-ball for the throw-out lever. That pivot-ball is a little ways inside the bellhousing, and difficult to reach.

So a squeaky pivot-ball won't be fixed by greasing inside the slave boot. But maybe moving it around helps a bit?

Seems like a squeaky slave-piston would be fixed by some grease in there, but it should last more than a couple days. Did you use silicone brake-grease? Normal lithium grease might get dissolved by the brake fluid?

I used "green grease" what the people at the store recommended when I asked for high temp. The noise was on some days and off others during the last week or so. Its an improvement when for months It had been on all the time. When I applied the grease the first time I did put some back in the bell housing (I have small hands to get it back there, though I had no idea what I was touching) and I have added to the slave boot I few times. Still nothing conclusive, but if it was the throw-out bearing would it be on and off or just whine until I got it fixed?

I think the throw-out bearing would keep doing it until fixed. You can't grease that without removing the transmission because it is literally right around the tranny input-shaft. Not even with small hands.

I don't know what "green grease" really is, but does the bottle/tube say "silicone" or "brake grease"? It's not just about temperature, it's also about dissolving in brake fluid.