Look on UK EBay as Vauxhall Cavalier MKIIs were the same thing and the manuals cover everything. I know as I have a 1987 Ascona 2.0i Hatchback and have sourced parts from England that fit the Vauxhalls. The only difference is the grille and emblems. All the running gear is very similar. I have sourced headligts, brake parts and wheel bearings and all fitted my Ascona.
I have heard that there is an american car based on this Ascona C . I cant remember now what is its name but I'll find it. It looks the same but it has a different front and back. Parts for this car are very available in europe as this car was very popular.
Mine is one of about thirty top specification ones brought in to New Zealand in 1987 as a sales test before the introduction of the 1988 Opel Vectra. It is an Opel and is a GT with 130 horsepower and capable of 127 mph. The only extra not on it is power steering - someone fouled up the order sheet, I am told.
Was looking for an Opel to use while my 1972 GT was in the body shop and found the Ascona forlornly sitting in a wreckers yard - made them an offer and drove it home. The handling was appalling - had three 14" wheels and one 13" on it.
The headlights were broken and it was an insurance write-off because the local GM dealers wanted $1,000 for two new units.
I found a pair on EBay for 9.99 GBP - yeh, less than ten quid!
Fitted a set of 15" X 6" BBS mags and 205-60 X 15 tyres that I had and it goes like a mad thing. It has kept me busy while waiting for the GT bodywork to be finished.
Never seen a 1975-81 Ascona in New Zealand and only one Manta. GM Holden had the market tied up for years and in the 1960s and 70s only Holden and Vauxhall were sold here.
There may have been a very few private imports.
From 1988 onwards Opel Vectras came into the market but were soon rebadged as "Holden" Vectras.
That's why the 1987 Ascona attracted me - it had an "Opel" badge and less than thirty were imported as a market test for the introduction of the Vectras the next year. For the previous twenty or thirty years Opel had not been available here.
My 1972 GT is also one of three known in the whole country and was privately imported by an American Woman living here. She brought it with her in the early 1980s.
The big wheels are quite a squeeze on the 1987 Ascona but the BBS Mags are fro a front wheel drive Japanese car of some sort (Mitzibushi I was told) and have an offset of ET45. The tyres just clear the suspension struts in the front and the front guards had to be "bulged" a bit to stop the tyres scraping
I'll put up a picture when I get one on the digital camera.