I don't know if it can help you in any way, but learn if the engine is used in other cars. You don't have to have the exact manual for repairing your car. For example, my gearbox is used in about 10 other models (honda, toyota, bmw, suzuki, isuzu) from other makers.
This allows me to get a manual for other car, covering the gearbox, buy cheaper rebuild kits (in USA they are very affordable, send by mail), etc.
Other example: the engine used in the Carlton (brazilian 1993-1998 omega) 2.0 is the same of kadett, ascona/monza, vectra; the 2.2 is the same of the s10 truck; the 4.1 is a tune-up of the opala (opel rekord); and so on.
Ah, yes: we make a lot of adaptions here; sometimes you get the same part from other car. Example: brake valve (the one that goes to brake assisting "pan") at store: omega: R$ 150,00, vw kombi: R$ 10,00 (R$ 1,00 = US$ 2,40). works and fit equally. I suspect it's the same part. This includes brake pads, anything. If you ask for "omega" the atendant will poke you in the eye (and you sometimes can see written in the part box "Fits: car 1, car 2, vw beetle, gm omega"... if you ask for the beetle part, it's a 1/10 ou 1/100 of the price...

If you want some omega a/b material (unfortunatedly, looks like there is no manual for omega diesel, so learn which other cars have the same engine and look for them), i have some 500MB of it. while i hate to have this stuff instead of an original printed book, it's better than nothing. :-/ :-/ :-/
HTH