front and rear disc mounting bolts

[limax2]

im guessing at m8x 30mm,

Not a bad guess but they are actually M8 x 25mm long.
Heating the head of the bolts a touch to break down the thread lock, as Gnasher suggests, has always worked for me. Also don't forget to use thread lock on your new bolts, unless they are already dry coated with it. (I don't know if the Yamaha ones are or not).