Slave leakage with levels between min and max?

If you do have a leak at the slave, you most likely won't be able to drive it (and wouldn't want to for safety reasons) so you shouldn't top off and go, plus the air that was sucked back into the fluid lines would make it nearly impossible to drive anyways. These are not expensive fixes for you to do and actually quite easy (provided that you have the tools and can get a friend to help you bleed the line), and by far not an expensive fix for a shop. Here in the states, I did my own for $60.00 for the slave and $10.00 for the fluid (I'll let you do the conversion).

If you had a sudden failure of the slave, you could have a failed master or slave cylinder that simply needs to be pumped manually (with the car off, not moving) to find where the fluid is coming out. The sudden failure could leave the leak blocked, but not seeping until you actuate the slave.