3rd Gear

[nosbod]

Hello,
Last month my gearbox cried enough so out it came and was rebuilt with all new internals. It was re installed and woks perfectly except that 3rd does not feel to fully engage and jumps out on over run. I swapped the tower for one that has given no trouble before so eliminating as a cause of the problem.
Does this mean as I fear that I must remove the box and disassemble it again or do any of you wise ones out there know differently?
Yours in expectation
John