How much are just the bushes genuine? And do you know someone who could press them into the existing wishbones?
Kevin
About 50-60 quid.
We have also recently discovered an uprated front bush which would fit (they are the same as the 7 series and mid 90's 5 series BMW's) and a poly version from the states (but the seller does not respond to emails!).
I know a man with a home made press and the set of drifts required to change the wishbone bushes... 
Hi Dudes,
Apologies for any unintended duplication...
Further to the above regarding a solution for the crap design of the Omega wishbone front pivot bush, a guy on one of the Cadillac forums posted a possible alternative BMW application that could fit the front of our wishbones.
According to
http://www.Meyle.com (Germany), the standard replacement bush for the Omega measures 58.5mm outside diameter, however, the guy on the Cadillac forum reckons a heavy duty BMW E34 (5 series) control arm bush, which is shown as 58.0mm outside diameter, will fit successfully. There are some pics on the Catera forum
Looking through Meyle's excellent website, I found another very similar heavy duty bush for a BMW E24 (6 series) listed at 58.5mm outside diameter - identical to the Omega spec.
Before we all get too excited, I have not yet determined if the centre bore or overall length of either of these bushes is compatible, but from the Cadillac forum it looks very promising.
Potentially better news is that
http://www.powerflex.co.uk list bushes for both BMW models in a solid polyurethane design incorporating a stainless steel crush tube around which the body of the bush can pivot. This should virtually eliminate lateral movement of the bush under braking conditions. It may even prolong the life expectancy of the standard vertical rear bush.
If anyone has a standard front wishbone pivot bush to hand from which they could provide exact measurements, please feel free to take up the baton with Meyle or Powerflex to determine viability.
In the meantime, I remain very optimistic with the Powerflex option, as it is likely only to need a minor alteration to a current product line. They're better at answering e-mails, too.
For anyone buying pattern replacement wishbones, I have found (IME) Veco branded items to be of satisfactory quality and readily available from numerous eBay sellers. I paid about £70 for a pair including postage sometime last year. Can't comment on longevity as gearbox expired just before following MoT was due, but it still felt OK up to then.
IMHO, I don't consider the significant extra outlay for "genuine" GM wishbones to be worth it for the marginal extra bush life.
Regards
Martyn H