There was action aplenty in the second stage when Christchurch's Matt Jensen - who was snapping at the heels of Gilmour - rolled his car into retirement and Gilmour reported brake problems.
That allowed Alex Kelsey to take the lead, but running out of fuel and later clutch failure put paid to the chances of the Coromandel teenager.
It was Chris West of Timaru who led after the third stage.
The high attrition rate continued when West retired in the fifth stage after damaging his front suspension, joining Gilmour who had suffered similar problems.
This stage was won by the rapidly improving Mason and he kept his yellow BNT Subaru STI in that position over the next two stages.
He sealed the championship title as a result.
Mason said he enjoyed the roads, which were twisty but not too tight.
"That's how we like them ... every corner was a challenge and grip levels were changeable."
Reflecting on their latest dual championship success - Sara having taken out the co-driver's title before the Gisborne event - Mason said they had a tough start to the year but had now won eight days in a row.
"It's been great, you never stop losing that will to win ... at the moment we are on a bit of a winning streak but every time we start a new day we think, what do have to do to win."
