Hi,
Which engine, year, milleage ? If the IRD breaks it generaly because of wrong tires, prop shaft in very bad condition, a VCU that is too stiff.
Ebay, you’ll find all what you want.
Also you can go and ask an other garage.
What are the symptoms ?
To remove the IRD you need to flush the IRD oil, flush the coollant, disconnect one drive shaft, and disconnect the prop shaft.
You need to be sure that the replacement IRD is in good condition before putting It back. Also all IRD don’t have the same ratio.
Why do you need to replace the IRD ? The rest of the transmission need to be in good condition before changing anything.
Regards.