Originally Posted by Mike Murrell

The EGR valve on the M103 engine in your 300-SEL is on the passenger side of the engine around cyl 3(approx.) - I will try to locate a web photo or one in my stash and post it.

This site won't allow posting any photo that has any size to it, so this is the best I can do. It's located where I mentioned up above:

https://www.pelicanparts.com/catalog/SuperCat/3368/MBZ_3368_EXHPIP_pg2.htm#item5