It may be worth renewing your g/box oil,also get someone to go through the gears with engine off and lubricate the selector shaft on top of g/box,the one you see moving up and down,they are bad for seizing up there just below the oil seal,if no better then the synchro hub in g/box may be worn,either put up with it or source a replacement g/box,good luck
cdc, June 2013