Newsreader that keeps messages and has a good text search

I've been using Thunderbird since Google Groups shut down, but I mostly enjoyed GG for the ability to quickly find messages by keywords.  I set TB to keep all messages, but it's search has been horrible and can't find hardly anything.  It also had a bug last week where it re-downloaded all the messages and now everything older than a week just comes up with an error.
Now Thunderbird has just decided there's no messages in this group, when I just downloaded the last 500 and started looking at them.
One of the other I'm looking for is the ability to retain all messages in a particular newsgroup,
Also built in spellcheck. I remember I tried a couple other newsreaders like x-news which is supposed to have a way to set up spellcheck but I couldn't get working.
I'm on PC, so running in Windows (10 right now) is a must.
I don't care at all about binaries as I'm using eternal-september.  I don't mind paying a little, and am considering Agent too.
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-Justisaur
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