Originally Posted by Mrmiata

Unless you can hear the starter free spinning I'd relax on this one.

Was the replacement starter a rebuilt or something that could have been marginal?
Did you ever investigate the "hissing sound"? Thinking that would be an exhaust
leak, and have to wonder if it hasn't created an issue?
One more thought... "terminals are clean"..is that just looking at them or have you
actually taken them loose and sanded the contact areas of the post and clamps to
insure a good connection?