There are quite a few Puma model Defenders in the 'crash damaged' category @ salvage yards. They (Defenders in general) are not designed to go fast, they pootle and to be honest they are excellent at pootling. Racing around just isn't what they do well. Of course you could upgrade the suspension, steering etc to make it a bit more stable on the road, but still it isn't a 'fast' car, it's a Defender.
Do you have the MT82 6 speed manual gearbox ?
They have a bit of a design fault (the premature wear of the output shaft) which can be 'upgraded' and is something i'd highly reccomend you do.
Winchester Gears PERFORMANCE MT82 6-Speed Gearbox At Winchester Gears, we proudly introduce our Performance MT82 Gearbox, a high-quality, upgraded
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We are able to supply the MT82 6 spd manual Defender gearbox as fitted to the 2007 onwards 2.4 / 2.2 TDCi engine. One of the common failures of the MT82 box is the premature wear of the output shaft due to a design fault. We have developed a kit to remedy this issue. You may
ashcroft-transmissions.co.uk
I would also start looking (in depth) at the chassis, bulkhead and other vunerable parts to make sure they are not being eaten by the tin worm and are protected against such an attack. At 11 years old this will help in ensuring it lasts another 11 years without major costs/repairs etc.
Removing bits, like the springs and shocks, A frame, front and rear radius and steering arms etc and refitting with new bushings, bolts/fasteners and plenty of grease will also pay dividends over time and make the car feel a lot 'tighter' on the road.
Of course non of this will make it look or sound any better, but it will be better, much better.
Changing the rear section as
@Wimblowdriver said is a really good option changing the whole exhaust system will cost a fortune and cause you headaches as well as diverting money away from what makes a 'good Defender' good.
