I can relate to your pain, as I'm currently very stuck on the seasonal event following it, the Focus in Madrid... Anyways, here is the tune I used to gold the Mini event:
Body
Rigidity Improvement
Power
No extra mods. Engine at 171 bhp naturally, from 3hrs of practice.
Transmission
Fully Customizable, 250 km/h or ~155 m/h
Drivetrain
Twin-Plate Clutch and Semi-Racing Flywheel, default/no LSD.
Suspension
Fully Customizable:
Ride Height front -25, rear -20
Spring Rate front 5.5, rear 10.0
Dampers (Ext) front 6, rear 7
Dampers (Com) front 1, rear 5
Anti-Roll bars front 4, rear 6
Camber Angle front 1.2, rear 0.6
Toe Angle front +0.25, rear -0.15
Brakes
Balance front 4, rear 3
Tyres
Comfort Soft
Couple of tips:
* Don't use 6th gear (you shouldn't need to with this tune).
* Don't use Traction Control or Active Stability because they will only slow the (already slow) Mini down for no benefit.
* Try to shift up about 500rpm before the interface readline as the Mini loses a lot of power at high revs.
* Lap times I needed to win it were around 1.05