I think someone said that Febi don't make parts. That is not correct. They have a large manufacturing facility in Germany. However, they are also a very large distributor of aftermarket parts. some of which no doubt are made in China.
The last Febi part I purchased, was a chain tensioner for my R107. Installed in 2008. Never a problem. I still have the box. Company name is Febi-bilstein (Not Febi Germany) and box sticker says Made in Germany.
It is well known that many popular brand name products are being illegally copied and produced in China. Some copies are so good, only the manufacturer would be able to tell.
They even copy complete cars!
Left side C-Class, Right side Geely Merrie 300
I had some discussions with Bosch regarding a fuel pump. They were suspicious that it might be a knock-off. They asked for and I sent them detailed pictures. It turned out it
was a Bosch pump, but made in Japan. However, they told me that many of their parts are being illegally copied. Something they are actively trying to stamp out.
I would suggest that if you have bad experience with a Febi product, that you contact Febi directly. You might get some satisfaction, but even if not, at least you will provide feedback that will allow FEBI to maintain their objectives of only supplying OE equivalent parts:
febi USA | Quality
It could be that their QC is not working as it should, but it could also be that you have been supplied fake products.
I would not buy off eBay. Buy from a reputable parts supplier. Won't guaranty anything, but will improve odds.