Connor
Hello,
If you happen to retire because of not repairing the car, your car will still be needing new parts for the next race.
Ideally, make sure to repair the car at least once every 2 races to reduce the risk of retirement.
If you're in a competitive league you really have to replace parts every race if you want to remain competitive. But like you say, every 2 races will enable you to safely finish every race, even if the races are Italy and Belgium, 2 of the hardest on the cars.