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Only 4000 over 10 years? Consider yourself lucky. I must have about 500,000.
This problem is not just that you can't see the email. You also can't move it (in WLM) or delete it. So if it is spam you're stuck with it.
Here's what I've learned over the years about OE/WLM. For one, it gets worse as folders get filled up with too many messages. So it's a good idea to put them into subfolders, even if just by date. I have to create them for every 3 months as they get up to about 15,000 messages at that point. I allow the current year to stay as one folder because it's a pain to have to search each quarter one at a time when I can't remember exactly when a message came in (or went out). That's one feature of OE I miss:searching a folder and its subfolders.
So the next thing I do, also since WLM won't seem to search the text of mails, is move ALL my mails older than a year or two into a separate folder on my hard drive and tell Windows Search to index that folder. I retain the subfolder structure from WLM in that folder for consistency. So if I am looking for something recent I use WLM, and if it is older I open Windows Explorer, go to the old email folder, and run a much faster search over from, to, subject and text of message. Just remember to close the search window when you are done, as it uses a lot of windows resources while open even after the search is complete. My extra old mail folder is about 30GB and it finds my results in less a minute. Your 4,000 emails will be fond in a few seconds at most I'd wager, and you can search on text. Which also negates some of the need to bother organizing the emails anyway since the search will do that for you.
When I have a crash of any kind and WLM is open (which is nearly always), something will probably get corrupted in the index. When this first happened to me, I thought I had lost all my emails. Trying to recover them with various tools took weeks, and only recovered about 10% of them. So the only recourse I had was to convince myself I didn't need all those emails anyway, and move on with my life. About a month later, while poking around on my hard drive, I found all these other folders with weird names of random letters and digits, sometimes appended to my old folder names, sometimes not. The reason I hadn't noticed these is that they were deeply deeply embedded in my folder structure. It turned out WLM had recovered all the mails and made new folders for me. It just hadn't bothered to tell me about them! Also, I suspect it was doing the recover in the background while WLM was open for other things, and with the amount of mail I had, this process may have taken days or weeks. But they were there. Not always segregated the way I did, but that was secondary.
Here's the solution: in WLM create a new folder, with no messages. Then, in Explorer, find the new folder that just got created, and the old folder with the bad index (this step might be VERY difficult because WLM creates deep trees). With WLM closed, simply copy the files from the old folder to the new one. Once it's done, reopen WLM and give it time to index the new folder (this can take a while if you have a lot of messages). They will all show as unread, and the From will contain both the name and email. But otherwise, all will be fine after that.
However, it may be that the bad messages don't show up in the new folder. This happens when the message is in the old index, but the file was already deleted.