1998 Mercury Sable power steering

Steering wheel hard to turn. Mechanic said there was a part that mercury quit making. Have to get at junk yard. I noticed it leaking and put jb weld on reservoir. Worked great for a while. Now its real hard to turn again. My aunt left the cap off reservoir and drove it for awhile before realizing it. Is there a less expensive way to fix this. When she added the fluid she didn't, let it idle for a while and the wheel was very hard to turn.