Re: Failed MOT- New bushes
Do you know which bushes at the rear need replacing? If you go with OE bushes you will need to replace the complete arms, whether it's the trailing arms, the upper wishbones, or the springpan arms. This is very expensive! Plus the rear suspension set-up is not straightforward - specialist knowledge is really needed to not only replace the kit but to set it all up correctly. For one thing they'll need to free off the adjusting rods for the rear toe as this is adjustable and needs to be set up correctly for your car to track properly.
And how do you know the garage knows what they're talking about? Have they worked on the 916-series cars before? If not, take it to a good specialist, get a second opinion, and plan the various options they may come up with to sort the problem. They may suggest:
1) Trailing arms. Powerflexing the trailing arms with the poly bushes. These work extremely well, and seem to last the distance from folks reporting on here. You don't need to replace the arms, the old bushes are removed for new powerflex ones, this is cheaper than buying new OE arms and will give you better performance.
2) Springpan arms. This are the ones most likely to have failed. Your car may have the solid bush type (if pre-JTS engine) and are prone to failure. Best way on this is to replace with the JTS/V6 arms, which are rose-jointed, and are excellent. You can powerflex these arms but there have been problems post-fitting (the arms take a lot of punishment and the powerflex bushes seem to suffer). New OE arms are very expensive, a dealer will quote you over £200 each, shop4parts have the cheapest quote I think at £150 each.
3) Upper wishbones. Unlikely to fail, as they don't do much anyway, if they fail it'll be the balljoint, so replace with OE wishbones if necessary.
Whatever you do make sure the garage knows what it's doing, if not take it to a specialist. You will bitterly regret it if you leave this specialist work to folks who don't know what they're doing.