If the oil level is low, fill it to requirement and then see if problem persists, if it does, then you need to consider the following which when causes the type of reaction you describe:
1. Replacement of the accummulator spring(s) in the valve body . The valve body is fairly easy to remove from under the battery compartment as it sits on top of the gearbox. 2. Replacement of the Governor seals. This can be accessed from the nearside front wheel and arch lining removed. Again, a fairly easy job. All this can be done with the gearbox in the car. What is the mileage on the car? Post your email and I will send you some technical info in this respect.