Why does it need to be original? is it going to be a legal issue for importation / road legality ? If so then you really need to identify what is construed as "original".
It has caught a lot of people out when importing to the USA, If you were going to take it back to Germany , what hurdles do you need to jump through?
The chances are that a large amount of 90 /110's from that era,( before 1990 are not technically defenders ) have had a change or two.
If , it is a legality issue then I would suggest finding a good source on here or online who works on the older models, off the top of my head there is Glencoyne Engineering
http://www.glencoyneengineeringltd.com/ who may have some info on a good one for sale.
Good luck.
Cheers