I've spent the last two days browsing through a book entitled "How to Rebuild and Modify Your Manual Transmission". Got it from Amazon.com for about $16. Very interesting reading. That looks like exactly what MBDoc says. If these trannies are similar to the one detailed in the book, this is one of two spring clips that sit inside a synchronizer assembly (one synchro assembly is shared for gears 1 and 2, another separate assembly is shared between gears 3 and 4, still another separate one exists just for overdrive. Reverse may or may not have one....probably not). The spring holds a small metal thingie in place inside a small hole in the synchro ring...the thingie is what allows the synchro to do what it's supposed to do. There are two springs and two thingies per synchro assembly. Could be that you have one of your synchro assemblies working with only one spring and one thingie instead of two. If this is actually a synchro spring, then you're talking about splitting the transmission case and rebuilding to fix it, I think.
Sorry about the anti-technical talk. The book is not in front of me. I can refer to it and be more specific if you'd like.

Brian

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Brian
1995 E320 wagon