I know you say it's been said it's not worth repairing the old unit but I can vouch for this company
http://www.caraudiorepairspecialists.co.uk
Used them last year to repair my father's Suzuki combined Radio CD unit when it would hold CD's ransom then turn from CD to Radio on its own.
I used a postal service but they're not too far from Bury.
Might be worth an ask to save wasting time, money and effort/frustration on fitting the aftermarket unit.