The previous owner of my Saab saw in his wisdom to put Ester synthetic oil in it as he had some turbo problems - which to be honest is a right pain because; a.it's seriously expensive stuff BUT, more annoyingly, b.you can't buy it anywhere I've found apart from mail order from Opie oils (who to be fair have alway been very quick in delivering).... but if you need to top up the oil you can't just pop into a motor factors....... a spot of Googling it suggests you can't just swap back to regular fully synthetic oil - informed opinions?

Drain it out and a gallon of flushing oil,

Yes you can switch back!
I wouldn't on a turbo'd car though. If you do you'll need to change it lots more and it'll save you no money and not protect your engine so well.
Trust in Opie oils, they are the dogs danglies and give sound advise. They may even tell you different to me and if they do it's probably 'cause they now something I don't!

You can usually buy ester based oils from any tuning/boy racer outlet but Opie will probably be cheaper. I run Fuchs Silkolene Pro S in my Celica, it's good stuff

Saabs built under the GM period have well known lubrication issues, that just don't surface if the car is run on fully synthetic.
Also any turbo engine needs a fully synthetic oil.

Any decent quality 5w/30 fully synthetic will do. Also change the oil at half the Saab mileage interval.

Use Havoline 5w/30 fully synthetic ---- Morrisons sell it from the petrol stations for 17 pounds for 5 ltr.

[Edited on 29/9/10 by britishtrident]