(warning - long post)
Hi EuJax... no worries bro... wasn't really asking u to justify la...
I too was initially worried about maintaining the E38. But, having poured through this forum and other BMW related sites (one good site is
www.e38.org), you get a general idea of what will break down and how much it will cost. 2 articles you should read are the Mar08 edition of BMWCars and Dec 05 edition of Bimmer magazine. They both contain buyer guide for E38.
Basically, there are 3 areas that can potentially give you the biggest headache (and most costly); engine, transmission and electrical/electronics.
Engine:-
Roadtax was a big decider of what engine I can afford. It was basically down to either the 728i (inline 6 M52B28) or the 730i (V8 M60B30). So that ruled out the 735i and 740i.
From a maintenance perspective, the inline 6 was cheaper to maintain compared to a V8. Also, an issue with both the M52 and M60 was the nikasil problems - infact, my biggest worry. But after understanding the problem (it was due to high sulfur content in the fuel used), avoiding UK recon models should do it.
Also, after talking to several BMW mech, they said the M52 is a more reliable engine and a cheaper fix should anything go wrong. Since it shared the same engine as the E36 328i and E39 528i (plenty in M'sia), parts were also generally easier to get and cheaper.
Transmission:
The transmission used in the E38 is generally trouble free. The older models do not have the steptronic gearbox. Just note that tho factory said its "sealed for life", it has been advised to change the oil regularly. Look for one that has oil change in its service history.
Electronics:
From what I have read, no major electronic problems that requires loads of $$$. Common problems include pixel display error and ABS sensor errors. Basic advise, make sure all the electronics are working when looking for a car.
Others:-
Other things to look out for is the suspension. Models that come with the self leveling suspension can be expensive to replace. Fortunately, it can also be replaced by std suspension system. Trims can be very expensive to replace and difficult to find. So, get one with the best condition trim available.
Once you got the above sorted, its just a matter of finding the best maintained / spec'ed model within your budget.
Last but not least, I'm still learning things about this car, so don't rely on my info exclusively. Do your own research then decide yourself.
Last note, sending to official dealer service centre (AB, Ingress, Sapura) will usually cost more. If your car is not under warranty, then going to a reputable mech is almost always cheaper. Search forum for recommendations. One name that always pops up for E38 is Albert. I personally have not used him tho, but because his shop is quite far from my place. Ask Sifu Vincent Hor for details....