7 series depreciate the fastest and are more heavily loaded as standard, and
in the past have represented excellent value for money when a few years old.

High mileage does not normally bother big 7's, but unfortunately those
fitted with the M60 V8 engine (pre ~1996) suffer the 'nikasil' problem.

The twin vanos straight 6 (M52?) engine allegedly suffer from O ring failure
in the high oil pressure valve timing mechanism.

Look back in this group for more info.

If they don't have service history run away, trust me.

The V8 cooling systems are cheaply made and the gearboxes have
"lifetime" fluid (change asap). I've had both and far prefer the M30 3.5
six to the V8s.

Watch for worn bushings and things, not dear in parts.

i picked up an e38 3.5l on a 98-plate for £3k here in UK.  before getting
this i was always a merc driver, but the 7-series is doing a good job of
changing my mind.  like another poster has said, the car *must* have a
service history.  apart from that, use your judgement about the previous
owner to decide whether that car has had everything it needs at the right
time.  the V8 can be comically frugal for such a big motor - but if you boot
it around alll the time you will need your own oil well.  from what i have
heard, the 728i is a good car, especially post-2000.

parts prices vary tremendously.  some are very expensive.  the e38 suffers
from a few model-specific faults, one being that the dashboard display
doesn't ... display.  £500 plus fitting.  the suspension bushings go at the
front, leading to alarming 'wobble' at certain speeds and under braking.
the bushes are cheap, garage labour is generally not.  tyres are expensive.

but they're lovely cars; on a recent trip to the continent, mine cruised
happily all day at 100+mph, and returned an average over 3,000 miles of
25mpg.

good luck.