I don't believe Microdol-X contained a mercapto compound. It contained a weaker type of anti-silvering agent. Perceptol is virtually identical in its working properties. I'd go with that over a home mix.
D25 is not the same. It achieves finer grain than D23 through a decrease in activity (lower pH) which means more solvent action. Think of it as D23 but with longer development times so that the sodium sulfite has longer to work on etching the silver grains.
Microdol and Perceptol are different. They are essentially D23 with the addition of sodium chloride to give finer grain.
It is also not clear how much Metol is in Microdol or Perceptol. Most people assume it to be 7.5g/litre because that is the most common amount used in D23. However this is not necessarily the case, and there were/are other versions of D23 with different Metol concentrations, such as 5g/litre.