Im just going to throw the idea to make partners something dynamic, something you will need to check every season, im kind of new to the game so i will be most likely wrong in 1 or two parts. (or something already work like i will say).
Engine, Tyres and Fuel partners have 3 stats. Experience, Image and Finance.
I think they already improve/degrade over time to make sure one partner will not be the best always season after season making it easy for the player to know who is the best after some trys. (If not they should).
A top of the line enginer partner will with time for example start to improve less and less its enginers. They are on top winning 5 years straight, this create a "ego" on them making harder for them to stay on top if another partner is also doing well.
But now the real part i wanted to talk about.
How about each month the partner send a letter to its customers asking what they need to improve in the tyre/fuel/engine? The partner will not say the "winner".
The winner stats would get +1, but there is a catch.
The engine have only a very small chance of not losing 1 point in another stat, and even a small chance of losing 2 points to get that +1.
Of course a engine will have a Max/Min cap to make sure a engine will not be useless. (The max/Min will change with partner finance/image/xp making sure a good company will most likely have a better engine, but thats not already a rule almost set in stone).
With chances to make sure you can´t renew contracts with little to no penality that would make each time you choose a partner something very important for your season.
Fuel would need to get another stat to make that work, but thats not that hard. A fuel also make your car response better and you can add Weight to the fuel. (A mix lighter or heavy), that will also add another feature to think about.
Liked? Dont liked? Something like that already working? ^^