take it elsewhere, get an independant report, then take it back.
they will NEVER find fault with one of their own sales.
if their is a fault with it, tell them you want a full refund, plus cost of independant report and finance agreement cancelled.
If you quote this, watch for a look of panic in their faces, ready...
Under the "sales of goods act 1979, section 2,subsection 14,paragraphs2, 2A,2B,2C,these goods are not fit for purpose, and therefore being returned and the contract will be cancelled"
sales of goods act i've quoted says,
2 - must be of satisfactory condition when being sold
2A - must be good quality,
2B - fit for purpose, free from "minor" defects, reliable
2C - any faults should have been drawn to your attention
if you go in, having done a bit of research, you should be able to get a better car for same money, or get all your money back
good luck