Mathepac has given some good advice.
You have to ask yourself:
"Could I deal with a lock up at 80 kph on a wet bend if the gearbox failed?"
Then you have to ask yourself:
"Could I deal with the consequences of running a possibly unroadworthy car, causing an accident and possibly injuring or killing people?"
You may find you're not covered by your insirance in the event of a claim.
Theie basic position is that you have to be a competent driver.
But the car may need to be "roadworthy" under the contract.
Take the car to a garage and ask them to check her over.
And don't stop with the gearbox.
Gearboxes seldom go first in terms of wear and tear.
Tyres, Brakes, Suspension, Clutches, Bearings, et cetera can all cause loss of control either in - or leading to - an emergency situation.
ONQ.