The S2 GTS25t had the ceramic turbine and plastic compressor, whereas the S1 (like mine) had the ceramic turbine and aluminium compressor. My mechanic checked mine recently while replacing the busted exhaust manifold studs and found it has the ali compressor, which can handle up to 1 bar.
I have no proof but have heard that "Type M" signifies Turbo. The different grille, skirts, front bar, wing were factory options (along with that narsty walnut-effect dash and different interior)