Hi Milan,
The pump may be OK but just have a sticky relief valve?
If you are game it may pay to check out the relief valve to see if you can ascertain if its just stuck open due to a bit of grit or somesuch.
Undo the hex headed fitting and remove it - be careful as it has a spring behind it. Next you need to get the pressure relief valve plunger out of the pump body. If its stuck expanding circlip pliers may do the trick.
If this fails and you are feeling brave place an oil drain container under the pump area, wrap the pump body loosely with a rag several times covering the open hole and start the engine, give it a rev and see if the piston loosens off and moves out of the pump body.
If it comes out you can inspect the surface for any seizure marks and dress it up as required. Push it in and out of the pump several times to check it is OK. If it feels OK clean, reassemble and try it.
Good Luck
Larry