Desmoquattro engines definitely suffered although the earliest (888 & early 916) seemed less prone.
The official line was that at some point Ducati outsourced the plating and the quality was not too great, they then claimed to have rectified the problem but despite these claims it still happened.
By Desmoquattro in a Monster that would be S4 and similar, later Testastretta 4v engines used a different rocker and so may not be as bad?
As for mileage, it could be just a few hundred or thousands, if the chrome was bad then it will flake, incorrect valve clearances don't help but even the best maintained will fail if the the rockers are not good.
The whole flaking rocker thing was a ****show with Ducati playing the slippery eel and denying responsibility whenever possible (despite the US getting free replacements for a while).
I contacted them years back about flaking rockers on my 916 and they said they were not aware of it being an issue, I had 9 fail in total.
If you have a Desmoquattro and want to put the problem to bed, send the rockers to Newman cams for them to modify and you'll never need worry again.
