2001 BMW X5 Transfer box chain jumping??/

As you refer to the job, do you mean inspecting for the cause or repairing the issue? Inspection would start with draining the oil from the transfer case and seeing if there is contamination in the oil. Repairing the unit might be as straightforward as replacement of the entire transfer case, and possibly less costly. If replacement sounds like the path of least resistance then call (619)444-2290 for Autobahn dismantling and talk to John or Sean.

Thanks so much for the help you gave. Are Autobahn dismantling in Germany??? I live in Spain.
Thanks Graham West

I apologize for my ignorance, as a moderator I may have made an assumption that your question was generated from somewhere in the United States. I do not know of any place in Europe that you could source the part you need. The E-mail address for Autobahn dismantling is parts@autobahnparts.com and they are located in the USA in El Cajon California @ 444 Vernon way zip code 92020