Grinding in 4th gear on 016 gearbox

[Adam Jansen]

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OK, now I have the oil plug finally open on my 016 gear box (Manually tranny on my 87 5KCSQ) I was indeed low on gear oil.  Small oil leak around the input shaft seal...

Even after filling there is still a grinding noise coming from the gearshifter when the car is in 4th gear.  If I push the shifter forward slightly right before neutral, the sound goes away...

Anyway, the noise wasn't there before I replaced the clutch. It just started when the gear oil level was low.
What did I break this time and how hard is it to replace?

Adam
Who is questioning his sanity for still holding on to his 87 5KCSQ