I'm have quite the same problem with my Suprema (Omega A Caravan/Estate).
Check if your transmission is the 4L30E. ........
We should be so lucky .... I assume you're on main land Europe somewhere because the UK never had the option of a 4.0 litre Omega A/Carlton. This forum is predomanantly V6 Omega B based.
Are you a member of Autobahnstomers? There's a lot of straight 6 knowledege there ...... aswell as Omegaforum members

Uh-oh... No bud... I don't mean four liter engine...

the "4L" means, for the trans maker "4-speed in line", like "3L" is the code for 3-speed. Check the GM parts (do a search fo "4L30E transmission" in google).
My very own car has a 3.0 line engine. It's the Opel engine. Here in Brazil, we also had a 4.1 Liter engine, for about 3 or 4 years, from a car named "GM Opala" (portuguese word for "Opal" -> said to be a cross of Opel + Impala - american car). This engine came from a truck line named "C-60/70" (12 tons I think), and equipped the pick-up trucks until these days, when such pickups came with diesels, then they ceased production.
It's a monster engine, very powerful at low rpm and it used to blow many of the 4L30E gear boxes, because of the torque... It was a carb-ed engine and the guys at lotus made the adjusts for (motronic?) mpfi. Check this:
opala engine: 6cyl, 4.1L ->
http://img230.imageshack.us/img230/4329/motor6cc2zx7.jpgmy car looks like this:
http://djjaragua.vilabol.uol.com.br/suprema.jpgomega engine: 6cyl, 4.1L ->
http://img253.imageshack.us/img253/8283/sudatsrn8.jpgthis was the last opala made:
http://djjaragua.vilabol.uol.com.br/opaladiplomata.jpgGreat car the opala... I have a opala caravan 1982, 2.5L 4-cyl, carb, 5speed. Good car... cheap to keep, simple mechanics, cost 10x less than omega to keep running...

back to the topic...

The transmission was also used in BMW, which went up to about 2.5liter -6cyl engines and 350Nmax... to the american market, it's a common transmission there, you can buy kits quite inexpensively to rebuild such trains.
Whoa! Hope this lights, rather than mess your brains!
