3/4 synchro

It almost sounds like you're not declutching far enough and making the brass work overtime.
Or possibly the oil is too thick,too thin, or wrong type. If you are using synthetic, get rid of it.And we don't need 140wt up here; I run 50/50; ATF/80-90 EP.
If your slider is new, you just need the brass rings...... and maybe not even those.

If you lived next door.....I could fix you up in a jiffy.