240D W-115 grinds going into 4th

[billhard]

I have taken my 1975 240D 4 speed out on a few test drives, so far both the clutch and trans work great in all ways but one. Going into fourth at high RPM's it grinds. I can shift it very slowly, like third to neutral wait a count of 2 then neutral to fourth and it won't grind.

I have pressure breed the clutch system from the slave up several times and feel pretty confident there isn't any air in the lines.

The shift rods were disconnected when I swapped engines so I guess they could be out of adjustment but it solidly goes into 4th.

I do not know the age of the slave or master cylinders, I could replace / rebuild them.

Would bushing present this problem?

Any ideas would be appreciated. Thanks