Mark Levinson - how to fix white logo paint that has peeled away?

Yes, if you plan to do it yourself call ML and get the exact paint color. White is very hard to match and even slightly off will look worse than it is now IMO.

What rockness said and use these or similar.
http://www.automotivetouchup.com/store/accessories/micro_dabbers.aspx

I used to sell and mix custom paint colors and there are a thousand different shades of white.  Each one had little bits of yellow, black, red...
Whatever it took to get the desired shade.  You will never match it exactly without knowing the precise paint code.  That said, I would leave it alone.  Just tell people you have a Mark Levinsor amplifier.  

Even if you found the right white, the paint on the amp would probably discolored after all of these years. It would likely be unnoticeable though. Just put the thin paint in the trough carefully with a pin as another said. 

If it is a water based paint you could also quickly wipe off any that strayed outside of the trough.

Or, and I know this is going to sound weird, but find a guy who collects and paints miniature soldiers. I have a friend who does this and what he can do with a paint brush is unbelievable.