You might be able to get some "feel" for it by turning the input shaft by hand and running it through the gears but that will tell you nothing about the syncro condition, the oil in it or anything else. Better at the very least to take off the top cover for a visual inspection and plan on replacing all the seals at the same time.
Before taking off the top cover, be sure to have a new gasket as you'll need one and they are available through
Olson's Gaskets. Ask them directly as I doubt it's listed on their site (few sites keep their online listing up to date) but I know for a fact that they have it. Most of their transmission gaskets are made by Best but Best sells only through authorized dealers although they have a few that they make themselves and their work is excellent, as is their delivery time.
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