From The E28 Wiki

Later Center Caps Don't Fit the Front

By wkohler, Mon Oct 06, 2008

Original thread: Center caps from later OE wheels don't fit up front!

Problem: I just picked up a set of newer OE wheels. The center caps went on the rear just fine, but don't fit on the front!

Cause: Your E28 is running the older-style spindle dust caps.

Solution: Purchase the newer-style "concave" dust cap!

Part number: 31206777789

[1]

The part is the same between left and right.

They're extremely inexpensive, as they cost about $2-$5 ea depending on where you get them. I'd give our endorsed vendors a shot first, though.

Simply pop your old ones out, and put these in. Give a nice whack with a rubber mallet and you're set!