Deores have seals but are not "sealed bearings"
And, yes your fork is a very likely culprit for your problem. A brake bridge night help a bit, but I think it is time for the upgrade fairy. The only problem might be if your bike is that old and you have cantilever brakes. There will be no housing stop on a new fork. So you would also have to upgrade your brakes to linear pulls. You also will need to have a threadless stem and headset.
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I am in the woods and I have gone crazy.