reliability of cars used cars in BMW 523,528 bracket

I "was" thinking of acquring a used BMW 523/528 SE of around 7 years old,
approx 100K miles.
This was becasue I have seen many of these in UK for around £5,000. But may
now be looking at a similiar Lexus GS300, Saab 9-5 2.3T or Audi A6 2.6.

I have in the past had a 7 yeard old 535SEi (Full Serivce History)/ 730 SEi
(part service history), and overall reliability was very dissapointing.
Engine's were OK, but many other "expensive" parts required replacing., e.g
Switchable gbox on 7'series (Ouch), front psngr window coming off rails,
headlight circuit blew, central locking malfunction, over heating, petrol
guage faulty. Basically the only enjoyment I got out of these two cars was
the road presence (when they were'nt in the garage).

Many people recommended to me to only buy BMW new, or get a used japanese
car, (Lexus, Toyota et al).

I am a "BMW guy" at heart, but my mechanic says a £5000 BMW 5 series would
be a downgrade in reliability compared to my current 11 year old Rover 620
SLI
(with Honda engine, worth about £300, which I havent spent anything on for a
year).

I find this very worrying....

Comments anyone...?