I can understand your concern, having an airbag go off in your face would not be a nice thing, nor would it be nice if it didn't fire when needed in a crash. If you have lost confidence in the dealers you have used, you could try another one, or you could contact Holden direct and request the company's involvement.

It's not possible to predict when your engine might expire; there are too many variables to take into account to even make an educated guess. Suffice to say that it's done a lot of cars and it's closer to the scrap yard than it is to the production line. You could have a 3.8-litre Holden V6 fitted, that was an option in the car when it was built, and would be the easiest engine transplant option. Fitting a Falcon six would involve too much surgery and I wouldn't recommend it. The best option if you want to keep the car, but cut running costs, would be to convert it to dual-fuel and run it on LPG.

HAVING the correct diff oil is important, particularly if you drive the car hard and really make the diff work. If they have used the incorrect oil because they failed to recognise the car had a limited-slip diff, I would pressure them to replace the diff. If that doesn't work, pursue the problem with Holden.