This is a 3.5 year old thread but I haven't done anything yet - I have newer gear of similar quality that works fine and I've been using that.
If I recall correctly, the repair price quoted from a Levinson authorized repair center for the ML 23 was about $2800. That was for repair and complete refurbishment, whatever that means. But while not warranteed it would likely work for decades more after that.
Now, that's maybe $500 more than working ML 23s are selling for. But I wouldn't buy any of those that haven't been refurbished because they are nearly certain to cook themselves to death at some point. I've read and heard it's basically inevitable due to their build.
Even so, I question the logic of spending $2900 to get something that I could only sell for $2300 or so since most folks wouldn't even trust I had it refurbished.
My ML 26 still works just fine other than the tape outs don't work and I suspect were intentionally disconnected. I don't know what the cost to refurbish that one would be.
In terms of that link, it seems like lots of the Levinson amps from that era have had issues and are starting to crap out. And the 2 "fully serviced" amps may not have been by an authorized dealer, so not sure if they would fully qualify as original Levinson amps.
I'm in no hurry. Would probably sell them for the right offer as I am more about reliability than vintage quality at the moment.