I have no problem with the egg whisk controls. They are merely icons of the best possible user interface for the purpose.
The Tardis, like much Gallifreyan technology such as the Doctor's magic wand, has a telepathic interface providing many services including translation and flight control.
The console/control room, like your computer interface, can be designed to appear in any way you like, according to the owner's whims. It doesn't even need to feature a console. The actual Tardis command interface is telepathic. The physical controls are a metaphor, rather than physically connected to anything, where the physical manipulation confirms the intended action of the user. This requirement for physical action is to prevent the mere thought of something happening without actually meaning it. For example, launching all the missiles, or setting the controls for the heart of the sun, could be a bad thing to do if the idea merely crossed your mind.
The physical controls metaphorically control the functionality the user expects/thinks/believes them to, so to an observer the slidy/tweaky/plungy object's apparent functionality can vary over time depending on the user.
The telepathic user interface is designed and "tuned" for Time Lords, which is why only Time Lords can fly a Tardis. That, and the security software.
The brake fluid reservoir of the current design is probably some metaphorical level indicator. Possibly of brake fluid.