Leak from power steering pump

Hi I have an opel 200is kadett, my only issue is that I have is that I have a leak coming from my power steering pump, when I drive it doesn't leak so much but as soon as I stop or park my fluid would run down quick then I have to top up again continuously

my power steering pump that sits by my fire wall, leaks continuously if I park or stop, the leak comes from underneath some kind of rubber seal on the right hand side, but it somehow doesn't leak if I were to be driving around, only when the cars parked, then it runs half empty and got to be topped up again, its happening everyday, when I idle her in the morning then it makes a weird noise and becomes stiff at the steering,

please give me some knowledge to how I could get it sorted out :-)

great site :-)