possible servo problem

My 1986 2.5 na diesel Seems to have a very hard brake pedal, and i feel like thee braking isnt the best at speed 30+ mph and when on a hill or stationary i have to apply the footbrake very hard then it might roll and i have to re apply more pressure, i do have a oil leak on the vacum pump so not sure to try a new gasket or change the servo?

It is possible for brake fluid to leak past the seals in your master cylinder into the rear end of your master cylinder ! This gives a very hard pedal feel as you are trying to compress the fluid trapped behind the actual piston !! The temporary cure is to crack open the pipe fitting to the rear brakes press your pedal to the floor and then lock pipe up try brakes and see if the pedal feels better !! If it does then you need a new master cylinder ! As it will fill up again after a while because of the seals!! Good luck