Help with 1968 4 speed transmission maintenance

I am finding the shifting a bit difficult, a grind here occasionlly, a hard push her, nothing consistent, other than reverse usually is the most frequent issue.

Thought I should check the fluid.

Is there a drain and fill plug separate? I haven’t looked yet.

Fluid suggestions, everything I see says be sure it is GL-4, not GL-5.

Anyone got links to videos or manuals?

Fill plug is on the passenger side of the toploader. Fill to the bottom of the bolt hole.
It’s possible that your blocking rings are beginning to wear.

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David Kee says to only use mineral oil. I would follow his recommendation.

It’s fill to spill. There are separate drain plug and fill plugs. Pretty simple. Jiffy lube will fill it for free.

Look at the linkage too. Poor adjustment and worn shift rod bushings will impact the shift quality.

Yes, you need GL-4 lubricant which is getting hard to find in retail stores.