325xi stick shifting problem

Shifting is a dream, except into third gear: always feels much stiffer. Twice last week my wife shifted into third and ground the gears. Takes too much care: too quick, feel a slap or kick against palm. Too slow, occasionally does not go into third; feels like missed the gate. Have driven sticks 39 years; our first BMW, after lots of Toyotas, Nissans, Volvos, great Integra, lousy Vega, abominable Voyager, and first car Beetle.