3rd gear grind

It won’t fix it.. but it ‘may’ prolong it.
It will be a rebuild required or try for an ok wreckers box

Good luck

decent rebuilders are few and far between

Make sure the oil you use is GL4. Do not use GL5 as it reacts with the syncro rings, especially the early ones.

I use redline MT90 with half a tube of Nylon N70 gear additive in the race car.
But the thing is it will not improve. You might just survive it longer.

Car breakers or wreckers usually give 7 day warranty.
If you can’t find someone to rebuild yours (1200 bucks here) get a wreckers box.

You ? No..

Someone experienced.. yes

Ok. I missed all that in your posts.
Good luck with that.