Brake Fluid Change

It’s not new. My Ford dealer tried to push for a brake fluid change every time I had my Focus serviced and that was annually. I had it done after about 3 years. 

Only you can decide but my feeling is that it would be included in the service if it was essential.

Good point about it being included in the service if essential, TW. I did have it done at the previous service when it was 'recommended'. That was at 29,500 miles. I've now only done a further 16,800 miles and the dealer has recommended it again.

Thinking back to may early years and maintaining my own cars, my dad, an Army vehicle mechanic, told me the fluid needed changing if the brakes started to feel a bit spongy and about every five years or so otherwise as the fluid absorbed water. I would have expected modern fluid to have improved in quality not, apparently, got worse.

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In my opinion the fluid is more likely to deteriorate on a low mileage car than a high as it becomes prone to collecting condensation, and near on 17k miles in two years isn’t particularly low mileage in my book, John,

Our car (Hyundai) has done about 7k in two years and the fluid was changed as it was included in the service. 🤷🏻‍♂️

In my opinion the fluid is more likely to deteriorate on a low mileage car than a high as it becomes prone to collecting condensation, 

Not disagreeing but it seems strange. A brake system is bled of air and is largely a contained system filled with brake fluid. The condensation comes from water vapour in the air. How does that enter the system? The only air fluid interface might be thought to be the breather hole in the reservoir. Any water vapour entering will be a very small amount and the water is lighter than the brake fluid.  

As above, brake fluid is hygroscopic ie absorbs water. Dealers & garages cover their bum by recommending a fluid change at 2 years irrespective of mileage. There are testers though that will check for water in the fluid ... how good they are, I've no idea. 

I'd be dubious of whether a complete change is ever done these day as there is a load of fluid in the ABS modulator that needs pumping through too ... 

+1 

Brake fluid can become hot under extreme conditions and it is designed to accommodate this however, if it regularly gets hot some constituents will be expended. It will discolour and possibly air bubbles will introduce more corrosion. in short is can deteriorate. However, modern braking systems are so well advanced and such great margins provided that non of these degrading processes are likely to the average motorist. The service engineer may recommend it but only after inspection. The service receptionist may offer all sorts of extras- new coolant sir? All the same - lovely extra profit. My advice is to stick strictly to the service schedule and no more or less. 

Good to see the armchair mechanics know more than the people who make the cars 

Some armchair mechanics actually are qualified and experienced in the subject. Even in the design and development of them. Even having a spent over 40 years in the profession. Not all, but some.