So I think there should be a feature where you can decide to either short shift or long shift wing your cars so that has to have a gearbox.
And each team is given 3 gearboxes per driver per season(because there's only 17 races IMO,maybe 4 gearboxes if new tracks are added).And if you use more than 3 gearboxes,each gearbox change gives you 5-place grid penalty(Good luck with your Yuji Ide driver that shifts 1 minute a gear).So after you qualified,if you have a grid penalty you will be demoted 5 places.Fox example:you qualifued 1st,you have a gearbox penalty you start 6th.And this can cause Reliability attribute to be more *cough* useful *cough*.And driving style also affects gearbox,PL1 harms gearbox less than PL5( so good luck trying to push like hell with Hard tires lol ).And,you know the more reliability points you have the gearbox will last longer,like each 10 points = +5% of the gearbox's reliability.And also gearbox under 50% tends to lose a gear or 2 so you have to DEAL WITH IT.And accept some lost of speed.(Or you could yolo and do a Senna Brazilian GP in 1991 with only 6th gear)