Hi all, right does the rear diff have certain driveshafts? or can any model driveshafts fit all model of diffs? Or are they coded like transmission?

e.g I have a 98 uk and My diff and driveshafts have been changed to a prodrive suretrack one (whatever that is) and the Diff is knackered so ive bought a new diff to fit my car (98 uk) but the driveshafts wont go in! The garage have said ive got the wrong driveshafts!!

Anyone shed some light on this please!

Ta all