Can any of the experts tell me if the rear diff is interchangeable between a 1980 124TE 4matic and other 124 estates or saloons? reason being mine is very noisy, whines at about 50-60 mph under load and it appears that only replacement will cure this and will need to look for repacement via a vehicle breaker here in Kent ,England. and is the job reasonably easy to do? Thanks in advance