Outer Limits 4x4 Board

I am after the bore size for an 89 GQ TD42 DX wagon with drum brake rear?
Mine has started to leak and the parts shop has told me there is 2 part numbers with different bore sizes and there is a $100 difference!!

Thanks in advance

Luxorr.

Shouldnt there be some cast numbers on the master cylinder ???
Use these they will help

just been through this,with my mk.
Mk aremasters are 23.81mm cost $110
early gq ,drum rear end 25.4mm cost $95
late model or didc rear end 26.99mm cost $145

Off e'bay but $15 post
I got a gq one for my mk for $92 at repco. next day
allways try for trade or get a mate who can get trade, the price mark up is BS