"There's a small hole in the radiator but the engine hasn't been overheating."
But Cox had problems off his own in the penultimate stage, going off the road at a high speed crest and completing the stage with the car "crabbing" along the road with the left rear wheel about 30 degrees from straight ahead.
"It was fifth gear over a crest and we hit the bank on one side and then the ditch on the other," said Cox.
"It's pushed the rear arm right into the subframe. There was enough time in the last service to give it good check, tighten everything up and we knew it would stay in place for the last stage."
That incident handed the lead back to Thomasen who sealed the rally win by setting fastest time of the short 3.7km TECT All Terrain Park stage.
"I think I learnt a bit today about pressure and it definitely taught me about the risks of running second hand tyres because I struggled for rear grip.
"But it's great to win my first rally, especially with a good battle against Sloan because he's a top driver and he's got plenty of experience."
Tauranga's Wayne Pittams brought his Subaru Impreza home in third position, surviving an off road moment in the final stage while Te Aroha teenager Lance Williams came fourth.
It was Williams' fourth rally and the first event he has finished. It was also his first outing in the ex-Robbie Leicester Subaru Impreza R4 and improving his pace by about 2secs per kilometre in the afternoon stages showed the potential of the new combination.
Rotorua's Ian Wood produced a spectacular drive to take the 2WD honours and finish fifth overall in his turbocharged Toyota Corolla DX. His closest 2WD rival was Tauranga's Phil Campbell who coaxed all the speed his Ford Fiesta R2 had to give on the fast forest roads and finished eighth.
The 47 strong field included 17 novices - drivers who had competed in less than three rallies - and it was Rotorua's Neil Dodds (Mitsubishi Galant VR4) who won the Novice award finishing 19th overall ahead of Tauranga's Mitch James (Toyota Starlet) who was 21st overall as 37 crews completed the event.
Tauranga Clubmans Rally - results:
1 Ben Thomasen/Megan Walker (Tauranga) Subaru Impreza WRX, 37min 26secs; 2 Sloan Cox/Steve Cox (Rotorua) Mitsubishi Lancer Evo X, 37m 34s; 3 Wayne Pittams/Malcolm Peden (Tauranga) Subaru Impreza WRX, 38m 41s; 4 Lance Williams/Raymond Bennett (Te Aroha) Subaru Impreza WRX R4, 39m 35s; 5 Ian Wood/Heather Wise (Rotorua) Toyota Corolla DX Turbo, 39m 56s; 6 Gareth McLachlan/Tanya Jackson (Hawke's Bay) Mitsubishi Galant VR4, 40m 13s; 7 Hugh Spence/Donna Elder (Gisborne) Subaru Impreza WRX, 40m 26s; 8 Phil Campbell/Shane Dufaur (Tauranga) Ford Fiesta R2, 40m 38s; 9 Ben Huband/Shaun Piper (Northland) Subaru Legacy RS, 40m 45s; 10 Doug Adnitt/Tony Mabbett (Northland) Subaru Impreza WRX, 41m 01s.