Dunno what Charlsey means by interlock plungers.
Gearlever waggles a rod back and forth and round. Rod waggles a selector yoke which waggles another rod this has a detent ball which drops into a groove, I doubt if it's this cos then all the gears would be difficult to get, any old how this shaft pushes a couple of selector forks about, selector forks push the gears about. The synchro hubs you've got three, one on first and second gear one on third and forth and one on fifth, Any how they have three slipper pads inside with a spring pushing them out these hold the outer hub bit central on the inner hub bit and helps hold an pull the gears into place anyhow these can wear and stick, and stop or make it difficult to engage gears. On mine it was second into third that was difficult, If I went from second to fourth then into third without releasing the clutch it went in a dream. Any old how it was the slipper pads that were worn, I'll bung a pic in my gallery of em if I get round to it. It's still worth setting the gear lever up to the haynes instructions fost though and having a look at the spring on the lever. And as I said before just moving the lever round a notch made selecting gears easier I was forever crunching First to second till I did mine.