Opel themselves actually replaced the rear window about 3 months after she bought the car..so that is done and everything else in your checklist has also been done lol, I have a nice pair of 15" 185 low profile tyres...the car has grip like hell!
I think my best bet then would be just to finance the corsa over 3years as Mfour suggested, then in 3 years time I will be in a much better position to buy myself a new car! (Alfa Romeo Giulietta...

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Thanks for all the replies guys! I just needed to figure out which option makes the most financial sense.
Peace.