The small seal in the gearbox shaft is cheap and easy to change, plus it can get damaged by removing the push rod.
The bearing behind it is also cheap but an absolute swine to remove so I wouldn't bother replacing it unless you know it to be bad.
Also, if fitting a new gearshaft seal, make sure it's in the right way round or the oil drips out into the clutch, potentially causing slippage but more embarrassingly smoke on startup after the oil has dripped onto your exhaust - don't ask how I know this...
