Alex Robbins is contributing editor at Telegraph Cars where, as well as responding to readers’ queries, he also contributes reviews of new and used cars, together with articles on buying and selling. 

His knowledge of the used car market informs his many buying guides relating to the best buys in particular sectors, with an emphasis on value for money.  Every week he will answer your questions on buying and selling, as well as solving your car problems, whether consumer or mechanical.

Do you have a motoring dilemma you’d like our expert to solve?  For consumer and used car advice, or car faults, email CarsAdvice@telegraph.co.uk and include your subscriber number. This week’s question…

Dear Alex…

My 2009 Audi A3 2.0 diesel has developed a small crack in the gearbox casing by the drain cap, which was pointed out to me by my local garage four months ago. They suggested I bring the car in again after two or three months for them to check the oil level to determine whether the casing was leaking and, if so, how badly. I did this and it needed a slight top-up.

The car has done 193,000 miles, but I want to keep it, as it is a pleasure to drive and it’s the greener option vs buying a new car. But I don’t want to pay a lot to have the gearbox replaced. I could just take the car in every three months for topping up (the cost last time was £32), but there is of course the risk the crack gets bigger and I lose all the oil. What should I do?

– PD

Dear PD…

You can pick up a good-condition second-hand gearbox for one of these for about £300 from a breaker, and I reckon it’ll cost you around £500 to get it fitted, with a clutch thrown in, depending on your garage’s labour charge. So let’s say £800 to get the problem fixed, versus £32 every three months to top up the fluid.

With the gearbox fixed, and with the mileage in mind, the car itself is probably worth around £1,500 or so. With a broken gearbox, however, it’s basically a spares car, as few people will want to bother doing such a big job on a car that leggy.

The maths, therefore, suggest that in all likelihood you’ll at least make any money you spend on the gearbox back if you sell the car, when compared with letting it go as it is.

Having said that, if I were in your shoes, I’d be tempted to go for the three-monthly top-up option for the time being, and wait to do the gearbox if and when the leak becomes more severe. Firstly, because the worst that can happen is that the gearbox gives out – an outcome that holds no fear for you if you’ve made your peace with replacing it anyway.

Secondly, it gives you a bit of time to save up for the gearbox job. And finally, if something else big goes pop in the meantime (which is not beyond the realms of possibility with a car of that mileage), you can reassess whether it’s still worth keeping the car – rather than being beholden to do so because you’ve just shelled out the best part of a grand on a replacement gearbox.

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