If I understand your question, this link might help, it should show the related part #'s

https://www.mboemparts.com/v-1999-mercedes-benz-e300--base--3-0l-l6-diesel/maintenance-and-lubrication--belts-and-pulleys

On your fuel leak, I had a similar problem when I bought my car and found it is one of the most common problems with it and similar diesels.

The plastic fuel lines and associated o-rings get old and brittle resulting in leaks. There are lots of posts on the subject if you do a few searches.

https://www.pelicanparts.com/catalog/SuperCat/3743/MBZ_3743_FULFUL_pg1.htm

look for 'fuel lines with fittings' and you should also source ' viton ' rubber o-rings for longer life