Greg:
I'm going to guess it's the synchro ring shared by first and second gear. If the 3 to 4 and 4 to 5 shifts are okay, then that gives more credibility to the bad synchro hypothesis. Plus that wire you fished out of the fluid (posted a while back) looked like part of a synchro assembly to me.
There are two main synchro ring assemblies in the trans. One is shared by gears 1 and 2, and the other is shared by gears 3 and 4. When shifting into and out of gears one or two, you are using that synchro to do it. If the assembly is screwed up, you may still be able to shift but it would be atypical, just as you describe. If so, then it's rebuild time.
Good luck.
Brian

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Brian
1995 E320 wagon